From fb33a96d373b8a8fc0abb4f6e5aed8cbafbbad8d Mon Sep 17 00:00:00 2001
From: RunasSudo <runassudo@yingtongli.me>
Date: Fri, 1 Jan 2021 22:26:57 +1100
Subject: [PATCH] Implement ERS97

---
 html/index.html               |  59 ++++--
 html/index.js                 |  59 +++++-
 pyRCV2/cli/stv.py             |  22 +-
 pyRCV2/method/base_stv.py     | 386 +++++++++++++++++++++++++---------
 pyRCV2/model.py               |   5 +-
 pyRCV2/numbers/__init__.py    |   6 +-
 pyRCV2/numbers/base.py        |   7 +
 pyRCV2/numbers/fixed_js.py    |   9 +-
 pyRCV2/numbers/fixed_py.py    |  11 +-
 pyRCV2/numbers/native_js.py   |  12 +-
 pyRCV2/numbers/native_py.py   |   6 +-
 pyRCV2/numbers/rational_js.py |  12 +-
 pyRCV2/numbers/rational_py.py |   6 +-
 tests/data/ers97.blt          |  51 +++++
 tests/test_aec.py             |   3 +-
 tests/test_csm.py             |   5 +-
 tests/test_prsa.py            |   5 +-
 17 files changed, 509 insertions(+), 155 deletions(-)
 create mode 100644 tests/data/ers97.blt

diff --git a/html/index.html b/html/index.html
index 0661e45..3ad277e 100644
--- a/html/index.html
+++ b/html/index.html
@@ -48,6 +48,7 @@
 					<option value="senate">Australian Senate STV</option>
 					<option value="wright">Wright STV</option>
 					<option value="prsa77">PRSA 1977</option>
+					<option value="ers97">ERS97</option>
 				</select>
 			</label>
 			<i class="sep"></i>
@@ -58,6 +59,20 @@
 		</div>
 		
 		<div id="divAdvancedOptions" style="display: none;">
+			<label>
+				Numbers:
+				<select id="selNumbers">
+					<option value="native">Native</option>
+					<option value="rational">Rational</option>
+					<option value="fixed" selected>Fixed</option>
+				</select>
+			</label>
+			<i class="sep"></i>
+			<label>
+				Decimal places (if Numbers = Fixed):
+				<input type="number" id="txtDP" value="5" style="width: 3em;">
+			</label>
+			<br>
 			<label>
 				Quota:
 				<select id="selQuotaCriterion">
@@ -73,33 +88,36 @@
 					<option value="hare_exact">Hare (exact)</option>
 				</select>
 			</label>
-			<i class="sep"></i>
 			<label>
-				<input type="checkbox" id="chkProgQuota">
-				Progressive quota
+				<select id="selQuotaMode">
+					<option value="static" selected>Static quota</option>
+					<option value="progressive">Progressive quota</option>
+					<option value="ers97">Static with ERS97 rules</option>
+				</select>
 			</label>
 			<i class="sep"></i>
 			<label>
 				<input type="checkbox" id="chkBulkElection" checked>
 				Bulk election
 			</label>
-			<label style="display: none;">
-				<input type="checkbox" id="chkBulkExclusion">
-				Bulk exclusion (NYI)
-			</label>
-			<br>
+			<i class="sep"></i>
 			<label>
-				Numbers:
-				<select id="selNumbers">
-					<option value="native">Native</option>
-					<option value="rational">Rational</option>
-					<option value="fixed" selected>Fixed</option>
-				</select>
+				<input type="checkbox" id="chkBulkExclusion">
+				Bulk exclusion
 			</label>
 			<i class="sep"></i>
 			<label>
-				Decimal places (if Numbers = Fixed):
-				<input type="number" id="txtDP" value="5" style="width: 3em;">
+				<input type="checkbox" id="chkDeferSurpluses">
+				Defer surpluses
+			</label>
+			<br>
+			<label>
+				<input type="checkbox" id="chkRoundQuota" checked>
+				Round quota to
+			</label>
+			<label>
+				<input type="number" id="txtRoundQuota" value="0" style="width: 3em;">
+				d.p.
 			</label>
 			<i class="sep"></i>
 			<label>
@@ -111,6 +129,15 @@
 				d.p.
 			</label>
 			<i class="sep"></i>
+			<label>
+				<input type="checkbox" id="chkRoundTVs">
+				Round transfer values to
+			</label>
+			<label>
+				<input type="number" id="txtRoundTVs" value="0" style="width: 3em;">
+				d.p.
+			</label>
+			<i class="sep"></i>
 			<label>
 				<input type="checkbox" id="chkRoundWeights">
 				Round ballot weights to
diff --git a/html/index.js b/html/index.js
index 7f404ad..5b4f726 100644
--- a/html/index.js
+++ b/html/index.js
@@ -1,6 +1,6 @@
 /*
     pyRCV2: Preferential vote counting
-    Copyright © 2020  Lee Yingtong Li (RunasSudo)
+    Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU Affero General Public License as published by
@@ -30,12 +30,16 @@ function changePreset() {
 	if (document.getElementById('selPreset').value === 'scottish') {
 		document.getElementById('selQuotaCriterion').value = 'geq';
 		document.getElementById('selQuota').value = 'droop';
-		document.getElementById('chkProgQuota').checked = false;
+		document.getElementById('selQuotaMode').value = 'static';
 		document.getElementById('chkBulkElection').checked = true;
 		document.getElementById('chkBulkExclusion').checked = false;
+		document.getElementById('chkDeferSurpluses').checked = false;
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = false;
+		document.getElementById('chkRoundTVs').checked = false;
 		document.getElementById('chkRoundWeights').checked = false;
 		document.getElementById('selSurplus').value = 'size';
 		document.getElementById('selTransfers').value = 'wig';
@@ -45,11 +49,14 @@ function changePreset() {
 	} else if (document.getElementById('selPreset').value === 'stvc') {
 		document.getElementById('selQuotaCriterion').value = 'gt';
 		document.getElementById('selQuota').value = 'droop_exact';
-		document.getElementById('chkProgQuota').checked = true;
+		document.getElementById('selQuotaMode').value = 'progressive';
 		document.getElementById('chkBulkElection').checked = true;
 		document.getElementById('chkBulkExclusion').checked = true;
+		document.getElementById('chkDeferSurpluses').checked = false;
 		document.getElementById('selNumbers').value = 'rational';
+		document.getElementById('chkRoundQuota').checked = false;
 		document.getElementById('chkRoundVotes').checked = false;
+		document.getElementById('chkRoundTVs').checked = false;
 		document.getElementById('chkRoundWeights').checked = false;
 		document.getElementById('selSurplus').value = 'size';
 		document.getElementById('selTransfers').value = 'wig';
@@ -59,13 +66,17 @@ function changePreset() {
 	} else if (document.getElementById('selPreset').value === 'senate') {
 		document.getElementById('selQuotaCriterion').value = 'geq';
 		document.getElementById('selQuota').value = 'droop';
-		document.getElementById('chkProgQuota').checked = false;
+		document.getElementById('selQuotaMode').value = 'static';
 		document.getElementById('chkBulkElection').checked = true;
 		document.getElementById('chkBulkExclusion').checked = true;
+		document.getElementById('chkDeferSurpluses').checked = false;
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = true;
 		document.getElementById('txtRoundVotes').value = '0';
+		document.getElementById('chkRoundTVs').checked = false;
 		document.getElementById('chkRoundWeights').checked = false;
 		document.getElementById('selSurplus').value = 'order';
 		document.getElementById('selTransfers').value = 'uig';
@@ -75,12 +86,16 @@ function changePreset() {
 	} else if (document.getElementById('selPreset').value === 'wright') {
 		document.getElementById('selQuotaCriterion').value = 'geq';
 		document.getElementById('selQuota').value = 'droop';
-		document.getElementById('chkProgQuota').checked = false;
+		document.getElementById('selQuotaMode').value = 'static';
 		document.getElementById('chkBulkElection').checked = true;
 		document.getElementById('chkBulkExclusion').checked = true;
+		document.getElementById('chkDeferSurpluses').checked = false;
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = false;
+		document.getElementById('chkRoundTVs').checked = false;
 		document.getElementById('chkRoundWeights').checked = false;
 		document.getElementById('selSurplus').value = 'size';
 		document.getElementById('selTransfers').value = 'wig';
@@ -90,19 +105,46 @@ function changePreset() {
 	} else if (document.getElementById('selPreset').value === 'prsa77') {
 		document.getElementById('selQuotaCriterion').value = 'geq';
 		document.getElementById('selQuota').value = 'droop';
-		document.getElementById('chkProgQuota').checked = false;
+		document.getElementById('selQuotaMode').value = 'static';
 		document.getElementById('chkBulkElection').checked = true;
 		document.getElementById('chkBulkExclusion').checked = false;
+		document.getElementById('chkDeferSurpluses').checked = true;
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = true;
 		document.getElementById('txtRoundVotes').value = '0';
+		document.getElementById('chkRoundTVs').checked = true;
+		document.getElementById('txtRoundTVs').value = '0';
 		document.getElementById('chkRoundWeights').checked = false;
 		document.getElementById('selSurplus').value = 'order';
 		document.getElementById('selTransfers').value = 'eg';
 		document.getElementById('selPapers').value = 'transferable';
 		document.getElementById('selExclusion').value = 'parcels_by_order';
 		document.getElementById('selTies').value = 'backwards_random';
+	} else if (document.getElementById('selPreset').value === 'ers97') {
+		document.getElementById('selQuotaCriterion').value = 'geq';
+		document.getElementById('selQuota').value = 'droop_exact';
+		document.getElementById('selQuotaMode').value = 'ers97';
+		document.getElementById('chkBulkElection').checked = true;
+		document.getElementById('chkBulkExclusion').checked = true;
+		document.getElementById('chkDeferSurpluses').checked = true;
+		document.getElementById('selNumbers').value = 'fixed';
+		document.getElementById('txtDP').value = '5';
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '2';
+		document.getElementById('chkRoundVotes').checked = true;
+		document.getElementById('txtRoundVotes').value = '2';
+		document.getElementById('chkRoundTVs').checked = true;
+		document.getElementById('txtRoundTVs').value = '2';
+		document.getElementById('chkRoundWeights').checked = true;
+		document.getElementById('txtRoundTVs').value = '2';
+		document.getElementById('selSurplus').value = 'size';
+		document.getElementById('selTransfers').value = 'eg';
+		document.getElementById('selPapers').value = 'transferable';
+		document.getElementById('selExclusion').value = 'by_value';
+		document.getElementById('selTies').value = 'backwards_random';
 	}
 }
 
@@ -308,14 +350,17 @@ async function clickCount() {
 			'options': {
 				'quota_criterion': document.getElementById('selQuotaCriterion').value,
 				'quota': document.getElementById('selQuota').value,
-				'prog_quota': document.getElementById('chkProgQuota').checked,
+				'quota_mode': document.getElementById('selQuotaMode').value,
 				'bulk_elect': document.getElementById('chkBulkElection').checked,
 				'bulk_exclude': document.getElementById('chkBulkExclusion').checked,
+				'defer_surpluses': document.getElementById('chkDeferSurpluses').checked,
 				'surplus_order': document.getElementById('selSurplus').value,
 				'papers': document.getElementById('selPapers').value,
 				'exclusion': document.getElementById('selExclusion').value,
 				'ties': document.getElementById('selTies').value,
+				'round_quota': document.getElementById('chkRoundQuota').checked ? parseInt(document.getElementById('txtRoundQuota').value) : null,
 				'round_votes': document.getElementById('chkRoundVotes').checked ? parseInt(document.getElementById('txtRoundVotes').value) : null,
+				'round_tvs': document.getElementById('chkRoundTVs').checked ? parseInt(document.getElementById('txtRoundTVs').value) : null,
 				'round_weights': document.getElementById('chkRoundWeights').checked ? parseInt(document.getElementById('txtRoundWeights').value) : null,
 			},
 			'seed': document.getElementById('txtSeed').value,
diff --git a/pyRCV2/cli/stv.py b/pyRCV2/cli/stv.py
index 5c21764..9c5f56b 100644
--- a/pyRCV2/cli/stv.py
+++ b/pyRCV2/cli/stv.py
@@ -29,11 +29,16 @@ def add_parser(subparsers):
 	
 	parser.add_argument('--quota', '-q', choices=['droop', 'droop_exact', 'hare', 'hare_exact'], default='droop', help='quota calculation (default: droop)')
 	parser.add_argument('--quota-criterion', '-c', choices=['geq', 'gt'], default='geq', help='quota criterion (default: geq)')
-	parser.add_argument('--prog-quota', action='store_true', help='progressively reducing quota')
-	parser.add_argument('--no-bulk-election', action='store_true', help='disable bulk election unless absolutely required')
+	parser.add_argument('--quota-mode', choices=['static', 'progressive', 'ers97'], default='static', help='whether to apply a form of progressive quota (default: static)')
+	parser.add_argument('--no-bulk-elect', action='store_true', help='disable bulk election unless absolutely required')
+	parser.add_argument('--bulk-exclude', action='store_true', help='use bulk exclusion')
+	parser.add_argument('--defer-surpluses', action='store_true', help='defer surplus transfers if possible')
 	parser.add_argument('--numbers', '-n', choices=['fixed', 'rational', 'native'], default='fixed', help='numbers mode (default: fixed)')
 	parser.add_argument('--decimals', type=int, default=5, help='decimal places if --numbers fixed (default: 5)')
+	parser.add_argument('--no-round-quota', action='store_true', help='do not round the quota')
+	parser.add_argument('--round-quota', type=int, help='round quota to specified decimal places')
 	parser.add_argument('--round-votes', type=int, help='round votes to specified decimal places')
+	parser.add_argument('--round-tvs', type=int, help='round transfer values to specified decimal places')
 	parser.add_argument('--round-weights', type=int, help='round ballot weights to specified decimal places')
 	parser.add_argument('--surplus-order', '-s', choices=['size', 'order'], default='size', help='whether to distribute surpluses by size or by order of election (default: size)')
 	parser.add_argument('--method', '-m', choices=['wig', 'uig', 'eg'], default='wig', help='method of transferring surpluses (default: wig - weighted inclusive Gregory)')
@@ -72,7 +77,11 @@ def print_step(args, stage, result):
 	print('Exhausted: {} ({})'.format(result.exhausted.votes.pp(2), result.exhausted.transfers.pp(2)))
 	print('Loss to fraction: {} ({})'.format(result.loss_fraction.votes.pp(2), result.loss_fraction.transfers.pp(2)))
 	print('Total votes: {}'.format(result.total.pp(2)))
-	print('Quota: {}'.format(result.quota.pp(2)))
+	
+	if args.quota_mode == 'ers97' and result.vote_required_election < result.quota:
+		print('Vote required for election: {}'.format(result.vote_required_election.pp(2)))
+	else:
+		print('Quota: {}'.format(result.quota.pp(2)))
 	
 	print()
 
@@ -97,6 +106,9 @@ def main(args):
 	else:
 		counter = WIGSTVCounter(election, vars(args))
 	
+	if args.no_round_quota:
+		counter.options['round_quota'] = None
+	
 	if args.ties is None:
 		args.ties = ['prompt']
 	
@@ -108,11 +120,11 @@ def main(args):
 			counter.options['ties'].append(TiesPrompt())
 		elif t == 'random':
 			if args.random_seed is None:
-				print('A --random-seed is required to use random tie breaking')
+				print('A --random-seed is required to use random tie breaking.')
 				sys.exit(1)
 			counter.options['ties'].append(TiesRandom(args.random_seed))
 	
-	counter.options['bulk_elect'] = not args.no_bulk_election
+	counter.options['bulk_elect'] = not args.no_bulk_elect
 	counter.options['papers'] = 'transferable' if args.transferable_only else 'both'
 	
 	# Reset
diff --git a/pyRCV2/method/base_stv.py b/pyRCV2/method/base_stv.py
index 2a6d57c..e24120b 100644
--- a/pyRCV2/method/base_stv.py
+++ b/pyRCV2/method/base_stv.py
@@ -61,15 +61,19 @@ class BaseSTVCounter:
 		
 		# Default options
 		self.options = {
-			'prog_quota': False,      # Progressively reducing quota?
 			'bulk_elect': True,       # Bulk election?
+			'bulk_exclude': False,    # Bulk exclusion?
+			'defer_surpluses': False, # Defer surpluses?
 			'quota': 'droop',         # 'droop', 'droop_exact', 'hare' or 'hare_exact'
 			'quota_criterion': 'geq', # 'geq' or 'gt'
+			'quota_mode': 'static',   # 'static', 'progressive' or 'ers97'
 			'surplus_order': 'size',  # 'size' or 'order'
 			'papers': 'both',         # 'both' or 'transferable'
 			'exclusion': 'one_round', # 'one_round', 'parcels_by_order', 'by_value' or 'wright'
 			'ties': [],               # List of tie strategies (e.g. TiesRandom)
+			'round_quota': None,      # Number of decimal places or None
 			'round_votes': None,      # Number of decimal places or None
+			'round_tvs': None,        # Number of decimal places or None
 			'round_weights': None,    # Number of decimal places or None
 		}
 		
@@ -97,9 +101,12 @@ class BaseSTVCounter:
 		Does not reset the states of candidates, etc.
 		"""
 		
+		self._exclusion = None # Optimisation to avoid re-collating/re-sorting ballots
+		
 		self.distribute_first_preferences()
 		
 		self.quota = None
+		self.vote_required_election = None # For ERS97
 		self.compute_quota()
 		self.elect_meeting_quota()
 		
@@ -110,7 +117,8 @@ class BaseSTVCounter:
 			self.exhausted,
 			self.loss_fraction,
 			self.total + self.exhausted.votes + self.loss_fraction.votes,
-			self.quota
+			self.quota,
+			self.vote_required_election,
 		)
 		__pragma__('noopov')
 		
@@ -162,8 +170,8 @@ class BaseSTVCounter:
 			return result
 		
 		# Insufficient winners and no surpluses to distribute
-		# Exclude the lowest ranked hopeful
-		result = self.exclude_candidate()
+		# Exclude the lowest ranked hopeful(s)
+		result = self.exclude_candidates()
 		if result:
 			return result
 		
@@ -205,13 +213,43 @@ class BaseSTVCounter:
 					self.exhausted,
 					self.loss_fraction,
 					self.total + self.exhausted.votes + self.loss_fraction.votes,
-					self.quota
+					self.quota,
+					self.vote_required_election,
 				)
 				__pragma__('noopov')
 				
 				self.step_results.append(result)
 				return result
 	
+	def can_defer_surpluses(self, has_surplus):
+		"""
+		Determine if the specified surpluses can be deferred
+		"""
+		
+		# Do not defer if this could change the last 2 candidates
+		__pragma__('opov')
+		total_surpluses = sum((cc.votes - self.quota for c, cc in has_surplus), Num(0))
+		__pragma__('noopov')
+		hopefuls = [(c, cc) for c, cc in self.candidates.items() if cc.state == CandidateState.HOPEFUL]
+		hopefuls.sort(key=lambda x: x[1].votes)
+		__pragma__('opov')
+		if total_surpluses > hopefuls[1][1].votes - hopefuls[0][1].votes:
+			return False
+		__pragma__('noopov')
+		
+		# Do not defer if this could affect a bulk exclusion
+		if self.options['bulk_exclude']:
+			to_bulk_exclude = self.candidates_to_bulk_exclude(hopefuls)
+			if len(to_bulk_exclude) > 0:
+				total_excluded = sum((cc.votes for c, cc in to_bulk_exclude), Num(0))
+				__pragma__('opov')
+				if total_surpluses > hopefuls[len(to_bulk_exclude) + 1][1].votes - total_excluded:
+					return False
+				__pragma__('opov')
+		
+		# Can defer surpluses
+		return True
+	
 	def distribute_surpluses(self):
 		"""
 		Distribute surpluses, if any
@@ -221,26 +259,40 @@ class BaseSTVCounter:
 		if any(cc.state == CandidateState.EXCLUDING for c, cc in self.candidates.items()):
 			return
 		
+		candidate_surplus, count_card = None, None
+		
 		# Are we distributing a surplus?
 		has_surplus = [(c, cc) for c, cc in self.candidates.items() if cc.state == CandidateState.DISTRIBUTING_SURPLUS]
-		
-		# Do surpluses need to be distributed?
-		if len(has_surplus) == 0:
+		if len(has_surplus) > 0:
+			candidate_surplus, count_card = has_surplus[0]
+		else:
+			# Do surpluses need to be distributed?
 			__pragma__('opov')
 			has_surplus = [(c, cc) for c, cc in self.candidates.items() if cc.state == CandidateState.PROVISIONALLY_ELECTED and cc.votes > self.quota]
 			__pragma__('noopov')
-		
-		if len(has_surplus) > 0:
-			# Distribute surpluses in specified order
-			if self.options['surplus_order'] == 'size':
-				has_surplus.sort(key=lambda x: x[1].votes, reverse=True)
-				candidate_surplus, count_card = self.choose_highest(has_surplus) # May need to break ties
-			elif self.options['surplus_order'] == 'order':
-				has_surplus.sort(key=lambda x: x[1].order_elected)
-				candidate_surplus, count_card = has_surplus[0] # Ties were already broken when these were assigned
-			else:
-				raise STVException('Invalid surplus order option')
 			
+			if len(has_surplus) > 0:
+				# Distribute surpluses in specified order
+				if self.options['surplus_order'] == 'size':
+					has_surplus.sort(key=lambda x: x[1].votes, reverse=True)
+				elif self.options['surplus_order'] == 'order':
+					has_surplus.sort(key=lambda x: x[1].order_elected)
+				else:
+					raise STVException('Invalid surplus order option')
+				
+				# Attempt to defer all remaining surpluses if possible
+				if self.options['defer_surpluses']:
+					if self.can_defer_surpluses(has_surplus):
+						has_surplus = []
+				
+				if len(has_surplus) > 0:
+					# Cannot defer any surpluses
+					if self.options['surplus_order'] == 'size':
+						candidate_surplus, count_card = self.choose_highest(has_surplus) # May need to break ties
+					elif self.options['surplus_order'] == 'order':
+						candidate_surplus, count_card = has_surplus[0] # Ties were already broken when these were assigned
+		
+		if candidate_surplus is not None:
 			count_card.state = CandidateState.DISTRIBUTING_SURPLUS
 			
 			__pragma__('opov')
@@ -262,7 +314,8 @@ class BaseSTVCounter:
 				self.exhausted,
 				self.loss_fraction,
 				self.total + self.exhausted.votes + self.loss_fraction.votes,
-				self.quota
+				self.quota,
+				self.vote_required_election,
 			)
 			__pragma__('noopov')
 			
@@ -300,24 +353,27 @@ class BaseSTVCounter:
 					self.exhausted,
 					self.loss_fraction,
 					self.total + self.exhausted.votes + self.loss_fraction.votes,
-					self.quota
+					self.quota,
+					self.vote_required_election,
 				)
 				__pragma__('noopov')
 				
 				self.step_results.append(result)
 				return result
 	
-	def exclude_candidate(self):
+	def exclude_candidates(self):
 		"""
-		Exclude the lowest ranked hopeful
+		Exclude the lowest ranked hopeful(s)
 		"""
 		
-		candidate_excluded, count_card = self.candidate_to_exclude()
-		count_card.state = CandidateState.EXCLUDING
+		candidates_excluded = self.candidates_to_exclude()
+		for candidate, count_card in candidates_excluded:
+			count_card.state = CandidateState.EXCLUDING
 		
 		# Handle Wright STV
 		if self.options['exclusion'] == 'wright':
-			count_card.state = CandidateState.EXCLUDED
+			for candidate, count_card in candidates_excluded:
+				count_card.state = CandidateState.EXCLUDED
 			
 			# Reset the count
 			# Carry over certain candidate states
@@ -342,12 +398,12 @@ class BaseSTVCounter:
 			step_results = self.step_results # Carry over step results
 			result = self.reset()
 			self.step_results = step_results
-			result.comment = 'Exclusion of ' + candidate_excluded.name
+			result.comment = 'Exclusion of ' + ', '.join([c.name for c, cc in candidates_excluded])
 			
 			return result
 		
 		# Exclude this candidate
-		self.do_exclusion(candidate_excluded, count_card)
+		self.do_exclusion(candidates_excluded)
 		
 		# Declare any candidates meeting the quota as a result of exclusion
 		self.compute_quota()
@@ -356,36 +412,87 @@ class BaseSTVCounter:
 		
 		__pragma__('opov')
 		result = CountStepResult(
-			'Exclusion of ' + candidate_excluded.name,
+			'Exclusion of ' + ', '.join([c.name for c, cc in candidates_excluded]),
 			self.candidates,
 			self.exhausted,
 			self.loss_fraction,
 			self.total + self.exhausted.votes + self.loss_fraction.votes,
-			self.quota
+			self.quota,
+			self.vote_required_election,
 		)
 		__pragma__('noopov')
 		
 		self.step_results.append(result)
 		return result
 	
-	def candidate_to_exclude(self):
+	def candidates_to_bulk_exclude(self, hopefuls):
 		"""
-		Determine the candidate to exclude
+		Determine which candidates can be bulk excluded
+		Returns List[Tuple[Candidate, CountCard]]
+		"""
+		
+		remaining_candidates = self.num_elected + sum(1 for c, cc in self.candidates.items() if cc.state == CandidateState.HOPEFUL)
+		__pragma__('opov')
+		total_surpluses = sum((cc.votes - self.quota for c, cc in self.candidates.items() if cc.votes > self.quota), Num(0))
+		__pragma__('noopov')
+		
+		# Attempt to exclude as many candidates as possible
+		for i in range(0, len(hopefuls)):
+			try_exclude = hopefuls[0:len(hopefuls)-i]
+			
+			# Do not exclude if this splits tied candidates
+			__pragma__('opov')
+			if i != 0 and try_exclude[len(hopefuls)-i-1][1].votes == hopefuls[len(hopefuls)-i][1].votes:
+				continue
+			__pragma__('noopov')
+			
+			# Do not exclude if this leaves insufficient candidates
+			if remaining_candidates - len(try_exclude) < self.election.seats:
+				continue
+			
+			# Do not exclude if this could change the order of exclusion
+			total_votes = sum((cc.votes for c, cc in try_exclude), Num(0))
+			__pragma__('opov')
+			if i != 0 and total_votes + total_surpluses > hopefuls[len(hopefuls)-i][1].votes:
+				continue
+			__pragma__('noopov')
+			
+			# Can bulk exclude
+			return try_exclude
+		
+		return []
+	
+	def candidates_to_exclude(self):
+		"""
+		Determine the candidate(s) to exclude
+		Returns List[Tuple[Candidate, CountCard]]
 		"""
 		
 		# Continue current exclusion if applicable
-		excluding = [(c, cc) for c, cc in self.candidates.items() if cc.state == CandidateState.EXCLUDING]
-		if len(excluding) > 0:
-			return excluding[0][0], excluding[0][1]
+		if self._exclusion is not None:
+			__pragma__('opov')
+			return self._exclusion[0]
+			__pragma__('noopov')
 		
 		hopefuls = [(c, cc) for c, cc in self.candidates.items() if cc.state == CandidateState.HOPEFUL]
 		hopefuls.sort(key=lambda x: x[1].votes)
 		
-		candidate_excluded, count_card = self.choose_lowest(hopefuls)
+		candidates_excluded = []
 		
-		return candidate_excluded, count_card
+		# Bulk exclusion
+		if self.options['bulk_exclude']:
+			if self.options['exclusion'] == 'parcels_by_order':
+				# Ordering of parcels is not defined in this case
+				raise STVException('Cannot use bulk_exclude with parcels_by_order')
+			
+			candidates_excluded = self.candidates_to_bulk_exclude(hopefuls)
+		
+		if len(candidates_excluded) == 0:
+			candidates_excluded = [self.choose_lowest(hopefuls)]
+		
+		return candidates_excluded
 	
-	def do_exclusion(self, candidate_excluded, count_card):
+	def do_exclusion(self, candidates_excluded):
 		"""
 		Exclude the given candidate and transfer the votes
 		Subclasses must override this function
@@ -401,18 +508,32 @@ class BaseSTVCounter:
 		self.total = sum((cc.votes for c, cc in self.candidates.items()), Num('0'))
 		self.loss_fraction.transfers += (self.total_orig - self.total - self.exhausted.votes) - self.loss_fraction.votes
 		
-		if self.quota is None or self.options['prog_quota']:
-			if self.options['quota'] == 'droop':
-				self.quota = (self.total / Num(self.election.seats + 1)).__floor__() + Num('1')
-			elif self.options['quota'] == 'droop_exact':
+		if self.quota is None or self.options['quota_mode'] == 'progressive':
+			if self.options['quota'] == 'droop' or self.options['quota'] == 'droop_exact':
 				self.quota = self.total / Num(self.election.seats + 1)
-			elif self.options['quota'] == 'hare':
-				self.quota = (self.total / Num(self.election.seats)).__floor__() + Num('1')
-			elif self.options['quota'] == 'hare_exact':
+			elif self.options['quota'] == 'hare' or self.options['quota'] == 'hare_exact':
 				self.quota = self.total / Num(self.election.seats)
 			else:
 				raise STVException('Invalid quota option')
+			
+			if self.options['round_quota'] is not None:
+				if self.options['quota'] == 'droop' or self.options['quota'] == 'hare':
+					# Increment to next available increment
+					factor = Num(10).__pow__(self.options['round_quota'])
+					__pragma__('opov')
+					self.quota = ((self.quota * factor).__floor__() + Num(1)) / factor
+					__pragma__('noopov')
+				else:
+					# Round up (preserving the original quota if exact)
+					self.quota = self.quota.round(self.options['round_quota'], self.quota.ROUND_UP)
 		__pragma__('noopov')
+		
+		if self.options['quota_mode'] == 'ers97':
+			# Calculate the total active vote
+			__pragma__('opov')
+			total_active_vote = sum((cc.votes for c, cc in self.candidates.items() if cc.state == CandidateState.HOPEFUL), Num('0')) + sum((cc.votes - self.quota for c, cc in self.candidates.items() if cc.votes > self.quota), Num('0'))
+			self.vote_required_election = total_active_vote / Num(self.election.seats - self.num_elected + 1)
+			__pragma__('noopov')
 	
 	def meets_quota(self, count_card):
 		"""
@@ -421,11 +542,11 @@ class BaseSTVCounter:
 		
 		if self.options['quota_criterion'] == 'geq':
 			__pragma__('opov')
-			return count_card.votes >= self.quota
+			return count_card.votes >= self.quota or (self.options['quota_mode'] == 'ers97' and count_card.votes >= self.vote_required_election)
 			__pragma__('noopov')
 		elif self.options['quota_criterion'] == 'gt':
 			__pragma__('opov')
-			return count_card.votes > self.quota
+			return count_card.votes > self.quota or (self.options['quota_mode'] == 'ers97' and count_card.votes > self.vote_required_election)
 			__pragma__('noopov')
 		else:
 			raise STVException('Invalid quota criterion')
@@ -451,6 +572,9 @@ class BaseSTVCounter:
 				self.num_elected += 1
 				
 				meets_quota.remove(x)
+				
+				if self.options['quota_mode'] == 'ers97':
+					self.elect_meeting_quota() # Repeat as the vote required for election may have changed
 	
 	# -----------------
 	# UTILITY FUNCTIONS
@@ -458,7 +582,7 @@ class BaseSTVCounter:
 	
 	def next_preferences(self, parcels):
 		"""
-		Examine the specified parcels and group ballot papers by next available preference
+		Examine the specified ballots and group ballot papers by next available preference
 		"""
 		# SafeDict: Candidate -> [List[Ballot], ballots, votes]
 		next_preferences = SafeDict([(c, [[], Num('0'), Num('0')]) for c, cc in self.candidates.items()])
@@ -546,6 +670,11 @@ class BaseSTVCounter:
 		if self.options['round_weights'] is None:
 			return num
 		return num.round(self.options['round_weights'], num.ROUND_DOWN)
+	
+	def round_tv(self, num):
+		if self.options['round_tvs'] is None:
+			return num
+		return num.round(self.options['round_tvs'], num.ROUND_DOWN)
 
 class WIGSTVCounter(BaseSTVCounter):
 	"""
@@ -569,28 +698,43 @@ class WIGSTVCounter(BaseSTVCounter):
 			if len(cand_ballots) > 0:
 				__pragma__('opov')
 				self.candidates[candidate].parcels.append(new_parcel)
-				self.candidates[candidate]._parcels_sorted = False
 				__pragma__('noopov')
 			
 			__pragma__('opov')
 			if self.options['papers'] == 'transferable':
 				if transferable_votes > surplus:
-					self.candidates[candidate].transfers += self.round_votes((num_votes * surplus) / transferable_votes)
+					if self.options['round_tvs'] is None:
+						self.candidates[candidate].transfers += self.round_votes((num_votes * surplus) / transferable_votes)
+					else:
+						tv = self.round_tv(surplus / transferable_votes)
+						self.candidates[candidate].transfers += self.round_votes(num_votes * tv)
 				else:
 					self.candidates[candidate].transfers += self.round_votes(num_votes) # Do not allow weight to increase
 			else:
-				self.candidates[candidate].transfers += self.round_votes((num_votes * surplus) / total_votes)
+				if self.options['round_tvs'] is None:
+					self.candidates[candidate].transfers += self.round_votes((num_votes * surplus) / total_votes)
+				else:
+					tv = self.round_tv(surplus / total_votes)
+					self.candidates[candidate].transfers += self.round_votes(num_votes * tv)
 			__pragma__('noopov')
 			
 			for ballot, ballot_value in cand_ballots:
 				__pragma__('opov')
 				if self.options['papers'] == 'transferable':
 					if transferable_votes > surplus:
-						new_value = (ballot_value * surplus) / transferable_votes
+						if self.options['round_tvs'] is None:
+							new_value = (ballot_value * surplus) / transferable_votes
+						else:
+							tv = self.round_tv(surplus / transferable_votes)
+							new_value = ballot_value * tv
 					else:
 						new_value = ballot_value
 				else:
-					new_value = (ballot_value * surplus) / total_votes
+					if self.options['round_tvs'] is None:
+						new_value = (ballot_value * surplus) / total_votes
+					else:
+						tv = self.round_tv(surplus / total_votes)
+						new_value = ballot_value * tv
 				
 				new_parcel.append((ballot, self.round_weight(new_value)))
 				__pragma__('noopov')
@@ -611,48 +755,49 @@ class WIGSTVCounter(BaseSTVCounter):
 		
 		count_card.state = CandidateState.ELECTED
 	
-	def do_exclusion(self, candidate_excluded, count_card):
-		if self.options['exclusion'] == 'parcels_by_order':
-			if len(count_card.parcels) > 0:
-				parcel = count_card.parcels[0]
-				next_preferences, total_ballots, total_votes, next_exhausted, exhausted_ballots, exhausted_votes = self.next_preferences([parcel])
-			else:
-				# TODO: Skip this entirely if this is the case
-				parcel = []
-			count_card.parcels.remove(parcel)
-		elif self.options['exclusion'] == 'by_value':
-			# Sort the ballots by value
-			if not count_card._parcels_sorted:
-				ballots = [(b, bv) for p in count_card.parcels for b, bv in p]
+	def do_exclusion(self, candidates_excluded):
+		# Optimisation: Pre-sort exclusion ballots if applicable
+		# self._exclusion[1] -> list of ballots-per-stage, ballots-per-stage = List[Tuple[Candidate,List[Ballot+Value]]]
+		if self._exclusion is None:
+			if self.options['exclusion'] == 'one_round':
+				self._exclusion = (candidates_excluded, [[(c, [b for p in cc.parcels for b in p]) for c, cc in candidates_excluded]])
+			elif self.options['exclusion'] == 'parcels_by_order':
+				c, cc = candidates_excluded[0]
+				self._exclusion = (candidates_excluded, [[(c, p)] for p in cc.parcels])
+			elif self.options['exclusion'] == 'by_value':
+				ballots = [(c, b, bv) for c, cc in candidates_excluded for p in cc.parcels for b, bv in p]
+				
+				# Sort ballots by value
 				__pragma__('opov')
-				ballots.sort(key=lambda x: x[1] / x[0].value, reverse=True)
+				ballots.sort(key=lambda x: x[2] / x[1].value, reverse=True)
 				# Round to 8 decimal places to consider equality
 				# FIXME: Work out a better way of doing this
-				count_card.parcels = groupby(ballots, lambda x: (x[1] / x[0].value).round(8, x[1].ROUND_DOWN))
-				count_card._parcels_sorted = True
+				if self.options['round_tvs']:
+					ballots_by_value = groupby(ballots, lambda x: self.round_tv(x[2] / x[1].value))
+				else:
+					ballots_by_value = groupby(ballots, lambda x: (x[2] / x[1].value).round(8, x[2].ROUND_DOWN))
 				__pragma__('noopov')
-			
-			if len(count_card.parcels) > 0:
-				parcel = count_card.parcels[0]
-				count_card.parcels.remove(parcel)
+				
+				# TODO: Can we combine ballots for each candidate within each stage?
+				self._exclusion = (candidates_excluded, [[(c, [(b, bv)]) for c, b, bv in x] for x in ballots_by_value])
 			else:
-				parcel = []
-			
-			next_preferences, total_ballots, total_votes, next_exhausted, exhausted_ballots, exhausted_votes = self.next_preferences([parcel])
-		else: # one_round
-			next_preferences, total_ballots, total_votes, next_exhausted, exhausted_ballots, exhausted_votes = self.next_preferences(count_card.parcels)
-			count_card.parcels = []
+				raise STVException('Invalid exclusion mode')
 		
+		#print([[bv / b.value for c, bb in stage for b, bv in bb] for stage in self._exclusion[1]])
+		
+		this_exclusion = self._exclusion[1][0]
+		self._exclusion[1].remove(this_exclusion)
+		
+		# Transfer votes
+		
+		next_preferences, total_ballots, total_votes, next_exhausted, exhausted_ballots, exhausted_votes = self.next_preferences([bb for c, bb in this_exclusion])
 		for candidate, x in next_preferences.items():
-			cand_ballots = x[0]
-			num_ballots = x[1]
-			num_votes = x[2]
+			cand_ballots, num_ballots, num_votes = x[0], x[1], x[2]
 			
 			new_parcel = []
 			if len(cand_ballots) > 0:
 				__pragma__('opov')
 				self.candidates[candidate].parcels.append(new_parcel)
-				self.candidates[candidate]._parcels_sorted = False
 				__pragma__('noopov')
 			
 			__pragma__('opov')
@@ -664,19 +809,30 @@ class WIGSTVCounter(BaseSTVCounter):
 				new_parcel.append((ballot, ballot_value))
 				__pragma__('noopov')
 		
+		# Subtract votes
+		
 		__pragma__('opov')
 		self.exhausted.transfers += self.round_votes(exhausted_votes)
 		__pragma__('noopov')
 		
-		__pragma__('opov')
-		count_card.transfers -= total_votes
-		__pragma__('noopov')
-		
-		if len(count_card.parcels) == 0:
+		for candidate, ballots in this_exclusion:
+			total_votes = Num(0)
+			for ballot, ballot_value in ballots:
+				__pragma__('opov')
+				total_votes += ballot_value
+				__pragma__('noopov')
+			
 			__pragma__('opov')
-			count_card.transfers -= count_card.votes
+			self.candidates[candidate].transfers -= total_votes
 			__pragma__('noopov')
-			count_card.state = CandidateState.EXCLUDED
+		
+		if len(self._exclusion[1]) == 0:
+			for candidate_excluded, count_card in candidates_excluded:
+				__pragma__('opov')
+				count_card.transfers -= count_card.votes
+				__pragma__('noopov')
+				count_card.state = CandidateState.EXCLUDED
+				self._exclusion = None
 
 class UIGSTVCounter(WIGSTVCounter):
 	"""
@@ -704,28 +860,43 @@ class UIGSTVCounter(WIGSTVCounter):
 			if len(cand_ballots) > 0:
 				__pragma__('opov')
 				self.candidates[candidate].parcels.append(new_parcel)
-				self.candidates[candidate]._parcels_sorted = False
 				__pragma__('noopov')
 			
 			__pragma__('opov')
 			if self.options['papers'] == 'transferable':
 				if transferable_votes > surplus:
-					self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / transferable_ballots)
+					if self.options['round_tvs'] is None:
+						self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / transferable_ballots)
+					else:
+						tv = self.round_tv(surplus / transferable_ballots)
+						self.candidates[candidate].transfers += self.round_votes(num_ballots * tv)
 				else:
 					self.candidates[candidate].transfers += self.round_votes(num_votes)
 			else:
-				self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / total_ballots)
+				if self.options['round_tvs'] is None:
+					self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / total_ballots)
+				else:
+					tv = self.round_tv(surplus / total_ballots)
+					self.candidates[candidate].transfers += self.round_votes(num_ballots * tv)
 			__pragma__('noopov')
 			
 			for ballot, ballot_value in cand_ballots:
 				__pragma__('opov')
 				if self.options['papers'] == 'transferable':
 					if transferable_votes > surplus:
-						new_value = (ballot.value * surplus) / transferable_ballots
+						if self.options['round_tvs'] is None:
+							new_value = (ballot.value * surplus) / transferable_ballots
+						else:
+							tv = self.round_tv(surplus / transferable_ballots)
+							new_value = ballot.value * tv
 					else:
 						new_value = ballot_value
 				else:
-					new_value = (ballot.value * surplus) / total_ballots
+					if self.options['round_tvs'] is None:
+						new_value = (ballot.value * surplus) / total_ballots
+					else:
+						tv = self.round_tv(surplus / total_ballots)
+						new_value = ballot.value * tv
 				
 				new_parcel.append((ballot, self.round_weight(new_value)))
 				__pragma__('noopov')
@@ -772,28 +943,43 @@ class EGSTVCounter(UIGSTVCounter):
 			if len(cand_ballots) > 0:
 				__pragma__('opov')
 				self.candidates[candidate].parcels.append(new_parcel)
-				self.candidates[candidate]._parcels_sorted = False
 				__pragma__('noopov')
 			
 			__pragma__('opov')
 			if self.options['papers'] == 'transferable':
 				if transferable_votes > surplus:
-					self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / transferable_ballots)
+					if self.options['round_tvs'] is None:
+						self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / transferable_ballots)
+					else:
+						tv = self.round_tv(surplus / transferable_ballots)
+						self.candidates[candidate].transfers += self.round_votes(num_ballots * tv)
 				else:
 					self.candidates[candidate].transfers += self.round_votes(num_votes)
 			else:
-				self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / total_ballots)
+				if self.options['round_tvs'] is None:
+					self.candidates[candidate].transfers += self.round_votes((num_ballots * surplus) / total_ballots)
+				else:
+					tv = self.round_tv(surplus / total_ballots)
+					self.candidates[candidate].transfers += self.round_votes(num_ballots * tv)
 			__pragma__('noopov')
 			
 			for ballot, ballot_value in cand_ballots:
 				__pragma__('opov')
 				if self.options['papers'] == 'transferable':
 					if transferable_votes > surplus:
-						new_value = (ballot.value * surplus) / transferable_ballots
+						if self.options['round_tvs'] is None:
+							new_value = (ballot.value * surplus) / transferable_ballots
+						else:
+							tv = self.round_tv(surplus / transferable_ballots)
+							new_value = ballot.value * tv
 					else:
 						new_value = ballot_value
 				else:
-					new_value = (ballot.value * surplus) / total_ballots
+					if self.options['round_tvs'] is None:
+						new_value = (ballot.value * surplus) / total_ballots
+					else:
+						tv = self.round_tv(surplus / total_ballots)
+						new_value = ballot.value * tv
 				
 				new_parcel.append((ballot, self.round_weight(new_value)))
 				__pragma__('noopov')
diff --git a/pyRCV2/model.py b/pyRCV2/model.py
index b5b6980..b501627 100644
--- a/pyRCV2/model.py
+++ b/pyRCV2/model.py
@@ -1,5 +1,5 @@
 #   pyRCV2: Preferential vote counting
-#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
 #
 #   This program is free software: you can redistribute it and/or modify
 #   it under the terms of the GNU Affero General Public License as published by
@@ -98,7 +98,7 @@ class CountCompleted:
 	pass
 
 class CountStepResult:
-	def __init__(self, comment, candidates, exhausted, loss_fraction, total, quota):
+	def __init__(self, comment, candidates, exhausted, loss_fraction, total, quota, vote_required_election):
 		self.comment = comment
 		
 		self.candidates = candidates # SafeDict: Candidate -> CountCard
@@ -107,6 +107,7 @@ class CountStepResult:
 		
 		self.total = total
 		self.quota = quota
+		self.vote_required_election = vote_required_election
 	
 	def clone(self):
 		"""Return a clone of this result as a record of this stage"""
diff --git a/pyRCV2/numbers/__init__.py b/pyRCV2/numbers/__init__.py
index e9a8daf..b01ea40 100644
--- a/pyRCV2/numbers/__init__.py
+++ b/pyRCV2/numbers/__init__.py
@@ -1,5 +1,5 @@
 #   pyRCV2: Preferential vote counting
-#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
 #
 #   This program is free software: you can redistribute it and/or modify
 #   it under the terms of the GNU Affero General Public License as published by
@@ -22,12 +22,12 @@ __pragma__('noskip')
 
 if is_py:
 	__pragma__('skip')
-	from pyRCV2.numbers.fixed_py import Fixed, set_dps
+	from pyRCV2.numbers.fixed_py import Fixed, set_dps, get_dps
 	from pyRCV2.numbers.native_py import Native
 	from pyRCV2.numbers.rational_py import Rational
 	__pragma__('noskip')
 else:
-	from pyRCV2.numbers.fixed_js import Fixed, set_dps
+	from pyRCV2.numbers.fixed_js import Fixed, set_dps, get_dps
 	from pyRCV2.numbers.native_js import Native
 	from pyRCV2.numbers.rational_js import Rational
 
diff --git a/pyRCV2/numbers/base.py b/pyRCV2/numbers/base.py
index 4c01801..423c1c5 100644
--- a/pyRCV2/numbers/base.py
+++ b/pyRCV2/numbers/base.py
@@ -116,6 +116,9 @@ class BaseNum:
 	def __le__(self, other):
 		raise NotImplementedError('Method not implemented')
 	
+	def __pow__(self, power):
+		raise NotImplementedError('Method not implemented')
+	
 	def round(self, dps, mode):
 		"""
 		Round to the specified number of decimal places, using the ROUND_* mode specified
@@ -214,6 +217,10 @@ class BasePyNum(BaseNum):
 		"""Implements BaseNum.__le__"""
 		return self.impl <= other.impl
 	
+	def __pow__(self, power):
+		"""Implements BaseNum.__pow__"""
+		return self._from_impl(self.impl ** power)
+	
 	@compatible_types
 	def __iadd__(self, other):
 		"""Overrides BaseNum.__iadd__"""
diff --git a/pyRCV2/numbers/fixed_js.py b/pyRCV2/numbers/fixed_js.py
index c0a4ccf..f0ccc75 100644
--- a/pyRCV2/numbers/fixed_js.py
+++ b/pyRCV2/numbers/fixed_js.py
@@ -21,6 +21,9 @@ Big.DP = 6
 def set_dps(dps):
 	Big.DP = dps
 
+def get_dps():
+	return Big.DP
+
 class Fixed(BaseNum):
 	"""
 	Wrapper for big.js (fixed-point arithmetic)
@@ -73,6 +76,10 @@ class Fixed(BaseNum):
 		"""Implements BaseNum.__le__"""
 		return self.impl.lte(other.impl)
 	
+	def __pow__(self, power):
+		"""Implements BaseNum.__pow__"""
+		return Fixed._from_impl(self.impl.pow(power))
+	
 	def round(self, dps, mode):
 		"""Implements BaseNum.round"""
-		return Fixed(self.impl.round(dps, mode))
+		return Fixed._from_impl(self.impl.round(dps, mode))
diff --git a/pyRCV2/numbers/fixed_py.py b/pyRCV2/numbers/fixed_py.py
index 0a23efc..29c9709 100644
--- a/pyRCV2/numbers/fixed_py.py
+++ b/pyRCV2/numbers/fixed_py.py
@@ -18,12 +18,17 @@ from pyRCV2.numbers.base import BasePyNum, compatible_types
 
 import decimal
 
-_quantize_exp = 6
+_dps = 6
+_quantize_exp = decimal.Decimal('10') ** -_dps
 
 def set_dps(dps):
-	global _quantize_exp
+	global _dps, _quantize_exp
+	_dps = dps
 	_quantize_exp = decimal.Decimal('10') ** -dps
 
+def get_dps():
+	return _dps
+
 class Fixed(BasePyNum):
 	"""
 	Wrapper for Python Decimal (for fixed-point arithmetic)
@@ -43,4 +48,4 @@ class Fixed(BasePyNum):
 	
 	def round(self, dps, mode):
 		"""Implements BaseNum.round"""
-		return Fixed(self.impl.quantize(decimal.Decimal('10') ** -dps, mode))
+		return Fixed._from_impl(self.impl.quantize(decimal.Decimal('10') ** -dps, mode))
diff --git a/pyRCV2/numbers/native_js.py b/pyRCV2/numbers/native_js.py
index 54a0b6c..3d89c3f 100644
--- a/pyRCV2/numbers/native_js.py
+++ b/pyRCV2/numbers/native_js.py
@@ -74,17 +74,21 @@ class Native(BaseNum):
 	
 	def __floor__(self):
 		"""Overrides BaseNum.__floor__"""
-		return Native(Math.floor(self.impl))
+		return Native._from_impl(Math.floor(self.impl))
+	
+	def __pow__(self, power):
+		"""Implements BaseNum.__pow__"""
+		return Native._from_impl(Math.pow(self.impl, power))
 	
 	def round(self, dps, mode):
 		"""Implements BaseNum.round"""
 		if mode == Native.ROUND_DOWN:
-			return Native(Math.floor(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
+			return Native._from_impl(Math.floor(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
 		elif mode == Native.ROUND_HALF_UP:
-			return Native(Math.round(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
+			return Native._from_impl(Math.round(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
 		elif mode == Native.ROUND_HALF_EVEN:
 			raise NotImplementedError('ROUND_HALF_EVEN is not implemented in JS Native context')
 		elif mode == Native.ROUND_UP:
-			return Native(Math.ceil(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
+			return Native._from_impl(Math.ceil(self.impl * Math.pow(10, dps)) / Math.pow(10, dps))
 		else:
 			raise ValueError('Invalid rounding mode')
diff --git a/pyRCV2/numbers/native_py.py b/pyRCV2/numbers/native_py.py
index d4c9e07..155b050 100644
--- a/pyRCV2/numbers/native_py.py
+++ b/pyRCV2/numbers/native_py.py
@@ -29,12 +29,12 @@ class Native(BasePyNum):
 		"""Implements BaseNum.round"""
 		factor = 10 ** dps
 		if mode == Native.ROUND_DOWN:
-			return Native(math.floor(self.impl * factor) / factor)
+			return Native._from_impl(math.floor(self.impl * factor) / factor)
 		elif mode == Native.ROUND_HALF_UP:
 			raise NotImplementedError('ROUND_HALF_UP is not implemented in Python Native context')
 		elif mode == Native.ROUND_HALF_EVEN:
-			return Native(round(self.impl * factor) / factor)
+			return Native._from_impl(round(self.impl * factor) / factor)
 		elif mode == Native.ROUND_UP:
-			return Native(math.ceil(self.impl * factor) / factor)
+			return Native._from_impl(math.ceil(self.impl * factor) / factor)
 		else:
 			raise ValueError('Invalid rounding mode')
diff --git a/pyRCV2/numbers/rational_js.py b/pyRCV2/numbers/rational_js.py
index 2f76fc7..089c94b 100644
--- a/pyRCV2/numbers/rational_js.py
+++ b/pyRCV2/numbers/rational_js.py
@@ -71,18 +71,22 @@ class Rational(BaseNum):
 	
 	def __floor__(self):
 		"""Overrides BaseNum.__floor__"""
-		return Rational(self.impl.floor())
+		return Rational._from_impl(self.impl.floor())
+	
+	def __pow__(self, power):
+		"""Implements BaseNum.__pow__"""
+		return Rational._from_impl(self.impl.pow(power))
 	
 	def round(self, dps, mode):
 		"""Implements BaseNum.round"""
 		factor = bigRat(10).pow(dps)
 		if mode == Rational.ROUND_DOWN:
-			return Rational(self.impl.multiply(factor).floor().divide(factor))
+			return Rational._from_impl(self.impl.multiply(factor).floor().divide(factor))
 		elif mode == Rational.ROUND_HALF_UP:
-			return Rational(self.impl.multiply(factor).round().divide(factor))
+			return Rational._from_impl(self.impl.multiply(factor).round().divide(factor))
 		elif mode == Rational.ROUND_HALF_EVEN:
 			raise NotImplementedError('ROUND_HALF_EVEN is not implemented in JS Native context')
 		elif mode == Rational.ROUND_UP:
-			return Rational(self.impl.multiply(factor).ceil().divide(factor))
+			return Rational._from_impl(self.impl.multiply(factor).ceil().divide(factor))
 		else:
 			raise ValueError('Invalid rounding mode')
diff --git a/pyRCV2/numbers/rational_py.py b/pyRCV2/numbers/rational_py.py
index c7b8dce..cfc5b6c 100644
--- a/pyRCV2/numbers/rational_py.py
+++ b/pyRCV2/numbers/rational_py.py
@@ -35,12 +35,12 @@ class Rational(BasePyNum):
 		"""Implements BaseNum.round"""
 		factor = Fraction(10) ** dps
 		if mode == Rational.ROUND_DOWN:
-			return Rational(math.floor(self.impl * factor) / factor)
+			return Rational._from_impl(math.floor(self.impl * factor) / factor)
 		elif mode == Rational.ROUND_HALF_UP:
 			raise NotImplementedError('ROUND_HALF_UP is not implemented in Python Rational context')
 		elif mode == Rational.ROUND_HALF_EVEN:
-			return Rational(round(self.impl * factor) / factor)
+			return Rational._from_impl(round(self.impl * factor) / factor)
 		elif mode == Rational.ROUND_UP:
-			return Rational(math.ceil(self.impl * factor) / factor)
+			return Rational._from_impl(math.ceil(self.impl * factor) / factor)
 		else:
 			raise ValueError('Invalid rounding mode')
diff --git a/tests/data/ers97.blt b/tests/data/ers97.blt
new file mode 100644
index 0000000..ab2800a
--- /dev/null
+++ b/tests/data/ers97.blt
@@ -0,0 +1,51 @@
+11 6
+35 1 2
+3 1 3 9
+11 1 3 6
+5 1 3 7
+6 1 3 8
+20 1 4 0
+7 1 4 9
+4 1 4 11
+8 1 5
+4 1 8
+1 1 10 5 7
+1 1 10 9
+18 1 11
+11 1 0
+81 2
+23 3 1 2 0
+2 3 1 2 7
+1 3 1 2 8
+1 3 1 0
+3 4 1 3 7
+1 4 8
+11 4 5 6
+3 4 2 0
+5 4 2 11
+1 4 3 0
+105 5
+91 6
+64 7
+5 8
+42 8 9
+12 8 7
+55 9
+2 10 5
+5 10 8
+14 10 9
+2 10 1 11
+90 11
+0
+"Smith"
+"Carpenter"
+"Wright"
+"Glazier"
+"Duke"
+"Prince"
+"Baron"
+"Abbot"
+"Vicar"
+"Monk"
+"Freeman"
+"ERS97 Model Election"
diff --git a/tests/test_aec.py b/tests/test_aec.py
index ff84aa7..fdf580f 100644
--- a/tests/test_aec.py
+++ b/tests/test_aec.py
@@ -1,5 +1,5 @@
 #   pyRCV2: Preferential vote counting
-#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
 #
 #   This program is free software: you can redistribute it and/or modify
 #   it under the terms of the GNU Affero General Public License as published by
@@ -47,6 +47,7 @@ def test_aec_tas19():
 	counter = UIGSTVCounter(election, {
 		'surplus_order': 'order',
 		'exclusion': 'by_value',
+		'round_quota': 0,
 		'round_votes': 0,
 	})
 	result = counter.reset()
diff --git a/tests/test_csm.py b/tests/test_csm.py
index 547c2b9..14200e0 100644
--- a/tests/test_csm.py
+++ b/tests/test_csm.py
@@ -43,7 +43,10 @@ def test_csm15():
 	
 	cands = {c.name: c for c in election.candidates}
 	
-	counter = WIGSTVCounter(election, {'exclusion': 'wright'})
+	counter = WIGSTVCounter(election, {
+		'exclusion': 'wright',
+		'round_quota': 0,
+	})
 	
 	# Round 1
 	result = counter.reset()
diff --git a/tests/test_prsa.py b/tests/test_prsa.py
index 96ab359..8db421a 100644
--- a/tests/test_prsa.py
+++ b/tests/test_prsa.py
@@ -1,5 +1,5 @@
 #   pyRCV2: Preferential vote counting
-#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#   Copyright © 2020–2021  Lee Yingtong Li (RunasSudo)
 #
 #   This program is free software: you can redistribute it and/or modify
 #   it under the terms of the GNU Affero General Public License as published by
@@ -45,7 +45,8 @@ def test_prsa1():
 	counter = EGSTVCounter(election, {
 		'surplus_order': 'order',
 		'papers': 'transferable',
-		'exclusion': 'parcels_by_order'
+		'exclusion': 'parcels_by_order',
+		'round_quota': 0,
 	})
 	
 	# Stage 1