When you vote tomorrow, cast a vote for nine City Council candidates in order of preference, and do the same for six School Committee candidates. Your number-one (first-choice) vote is the most important one in both races, but your ballot will count the most if you vote for as many candidates as permitted--nine for City Council and six for School Committee.
Under Cambridge's proportional representation system, the ballots must be counted, redistributed, and recounted many times to decide the election. In the Council race, election commissioners first establish a "quota" of votes necessary to elect a Councilor based on the number of ballots cast.
Candidates with a quota of more number-one votes are automatically elected. To seat the Council, the election commissioners divide up the ballots among the candidates by number-one votes.
The candidate with the most number-ones is seated first. Then, the commissioners take away ballots from this person's pile, picking them at random, until only a "quota" is left to the newly elected councilor's credit.
These "surplus" ballots (the ones taken away) are called the candidate's "transfers." Each of these is redistributed to the candidate who appears as the voters second choice.
The same process is done for the candidate with the second most number of votes, and so on. Each time, a transferred ballot counts for the first candidate appearing on it who has not already been elected.
Eventually the election commissioners come to a candidate who has less than a quota of ballots to his or her credit. At this point they eliminate the candidate with the fewest number-one votes and transfers, and redistribute the ballots he or she had received.
They do the same for the candidate with the next lowest total, and continue to the next candidate, until nine Councilors or six School Committee members are elected.