Forty-two years ago, the city of New York conducted its last election under the voting system known as proportional representation.

The city of Cincinnati, Ohio scrapped the innovative voting system a few years later. As did the city of Worcester, Mass. In fact, since the 1940s, every American city that has adopted the highly-touted system for ensuring minority representation has repealed it.

EXCEPT Cambridge.

With the exception of New York City's community school board elections, Cambridge is the only municipal government in the U.S. to use proportional representation--typically known as PR, according to the New York-based Institute of Public Administration.

In this era of exit polls and televised results, city residents still watch officials spend more than a week counting their preferential ballots to determine the outcome of City Council and School Committee contests.

IN theory, PR is designed to make sure the fringe gets a voice in situations where traditional voting methods split two parties along a few mainstream issues. In Cambridge, candidates only need to receive support from one-ninth of the electorate, rather than a majority.

Although several systems of voting--including those used in most European countries--are a form of PR, the variant that American cities have historically used is the one Cambridge employs--the single transferable ballot.

Under this system, candidates for council and school committee do not represent a specific district but are elected at large, Voters rank candidates in order of preference--first choice, second choice, and so on.

When votes are counted, candidates with more than a specific quota are declared elected. Election officials then look at the candidate's "surplus"--the number of votes in excess of the quota--and "transfer" them to the next choice.

If no one is above the quota, election officials transfer the votes of those candidates with the lowest number. This process repeats itself until the proper number of candidates is elected.

PR arrived in Cambridge in 1941, carried in by a wave of good-government reform and prompted by a scandal that nearly bankrupted the city and sent the mayor to jail.

At that time, the new Plan E charter stripped the mayor and City Council of almost all executive power, vesting it in the city manager, to be appointed by the council. The old voting system of wards and precincts was revamped and replaced with PR.

Many large industrial cities--where machine politics, patronage and one party rule were the norm--instituted such changes, hoping to ensure that everyone got a voice in government.

"It basically was a real good-government thing," says Paige E. Bigelow of the Institute of Public Administration. "It basically meant that every person's vote really did count--that every member of the electorate had a person whom they really did vote for."

But although the PR system has withstood several challenges at the polls over the last 48 years, people in Cambridge still grumble about it from time to time.