SAN DIEGO -- An election watchdog group is asking for a recount of last week's mayoral vote, saying there are serious questions about the reliability of the computer system used to count ballots.

Major concerns are coming from Brina-Rae Schuchman and the Citizens Audit Parallel Election project.

Last Tuesday, the non-partisan group camped outside polling booths. After voters cast a vote inside, they were asked to vote a second time outside, swearing the votes they cast were the same.

This was all done to check the reliability of the Diebold tabulating machine.

They collected more than 1500 of those ballots from 11 different precincts, and from these they came to a conclusion.

"It's an indication of some of the problems we've been talking about the last couple years," said Schuchman.

According to the group's analysis, their count consistently differed from the registrar's tally, between 2 and 4 percent. These are numbers they consider significant.

Project members concede that not everyone that swore about their vote was necessarily telling them the truth, but say their statisticians factored that in, and still found the discrepancy peculiar.

The group says it plans on asking and paying for a partial recount.

"If it comes out equal, terrific, but our numbers indicate that's not a high probability," Schuchman said.

Critics have raised questions about security and reliability of the system, but state elections officials continue to defend it.

"These are the tools we are given to work with. The state has certified them and deemed them reliable," said registrar of voters Michael Haas.

Other Diebold products continue to come under fire.

Last week, the state rejected the touchscreen machine because of reliability problems. And last March, glitches in that system prevented many San Diegans from voting.

The recount will likely begin in mid-August.

The group says if the discrepancy is big enough, it may ask to invalidate the election.