Although the polls in the city election close tonight, results won't be in for another week or so.

In a system known as Proportional Representation (PR), which distinguishes Cambridge from any other city in the United States, workers for the Election Commission take days to count each ballot by hand.

"It [usually] takes five and a half business days," former Election Commissioner Edward J. Samp, of the counting process. "[We] start on a Wednesday or the day following the election and finish next Tuesday."

PR arrived in Cambridge in 1940 as part of "Plan E," a form of city government approved by the Massachusetts legislature which features a strong city manager, a nine-member city council and a semi-autonomous seven-member school committee, according to the Election Commission.

Proponents of the system, which allows voters to rank candidates in terms of preference, say it was intended to combine minority representation along with majority control in the lawmaking body.

"One of the attractive features of the system is that it broadly represents the range of people in Cambridge," says Professor of Government Kenneth A. Shepsle.

Under PR, voters can cast ballots for as many candidates as they desire, ranking them according to preference.

A complicated formula is used to determine a quota (usually about 10 percent of the vote). Candidates who receive that number of votes or more are declared officially elected.

Ballots marked first for a candidate who exceeds the quota re then to the next designated candidate (that is, the next numbered choice).

PR replaced a city government run by a popularly elected mayor, a city council of 15 elected in both at-large and ward districts, and a school committee of seven.

Samp, a long-time Cambridge resident, says the implementation of PR was an attempt to reform what was widely perceived as a corrupt city government.

"Many people felt that the local government was corrupt...and they wanted to get rid of it. They elected Plan E...to improve the honesty and efficiency of city government," he said.

Although other American cities have attempted this form of government, Cambridge alone has retained it.

The system, influenced by the philosophy of John Stuart Mill, was developed in Europe during the 19th century through the philosophy of John Stuart Mill and used in Cincinatti, Ohio, during the 1950s.

It was also used in Worcester, Medford, Lowell and Newburyport, Mass. until being voted down under the "Home Rule" amendment, according to a report distributed by the Election Commission.