It is only fitting that in this uniquely heterogeneous city there should be a unique system of voting: Proportional Representation (PR). Designed to give minority candidates a better chance in elections, PR was used by some 25 American cities at the turn of the century. However, it was abandoned almost everywhere when it worked too well, aiding the election of unpopular minorities.

But minorities are the life-blood of Cambridge--blacks, landlords, the rich, Italians, students, the poor, Catholics, intellectuals, etc. Since each minority is equally unpopular and equally strident in its demands for a share of political power, PR remains in Cambridge, its last pure bastion in the country.

The system works as follows. A voter is given two long paper ballots listing the names of all candidates for city council and school committee. He indicates his choices not with an X, but by ranking them in preferential order (1, 2, 3, etc.). Although theoretically he could assign a number to every candidate in the race, most voters designate only four or five choices.

The ballots are then sorted according to the number one votes. To win election, a candidate must have a certain quota of votes. That quota is derived by dividing the number of ballots by the number of seats to be filled plus one, then adding one to the quotient. Thus if 30,000 votes are cast on Tuesday, the quota for election to the nine-member city council will be 3001. The quota was established to help minority candidates but still make the election more than a matter of chance.

Once a candidate has surpassed the quota, his excess votes will be re-distributed among the candidates who were marked number two on his ballots. If those candidates also go over the quota, the ballots will be withdrawn again and credited to the contenders in the third position. This process continues until nine council candidates and six school committee aspirants have reached the quota figure.

The counting goes on for several days, under the watchful eyes of the candidates, their supporters, and various old pols who emerge for this biennial spectacle. There is much anxiety and knashing of teeth, as candidates who do not have enough number one votes must hope that they played second fiddle in the minds of other voters.