Cambridge elections would not be half as exciting or unpredictable without the unique institution of proportional representation. This is the only city in the United States--and possibly the world--that still relies on this form of electoral roulette. Proportional representation aims to insure that all of the city's groups, regardless of their geographic concentration, have some power in city politics.
The system works to some extent: in city-wide elections over the past few years liberals have managed to get a disproportionate four or five city council seats, and there has usually been one black on the council since the mid-60s.
Elections are bi-partisan, and there are no primaries. In the general election, voters list all city council and school committee candidates in numerical order, starting with one for their first choice. Voting is probably the easiest part of the proportional system, as the polls are open for only one day and it usually takes at least two to hand count the ballots.
The election commission sets the quota, which is one-tenth plus one of all votes cast for council seats and one-seventh plus one for the school committee.
First, they tally all the number one votes, and if any candidate makes the quota, he is immediately elected (something only Walter J. Sullivan can do). His surplus votes go to whoever the voter marked number two. Candidates on the bottom of the totals are eliminated, and the women keep redistributing the ballots until nine council and six school committee candidates make quota.
This system encourages a variety of strategies, most notably slate politics. Liberals can field a large number of candidates without fatally diluting their strength by grouping under the Cambridge Convention banner and capitalizing on their cross-over vote strength. Since every ballot will eventually count for some candidate, left-leaning voters can vote for someone with little chance of winning, and still protect their interests.
Candidates, whether they are on a slate or not, always campaign for the "number one vote" since two-thirds of the ballots generally don't transfer. There is a minimum of strategic maneuvering because on one ever understands all of the options. Whatever else it does, proportional representation insures that the bookies will never make a killing.