Simple arithmetical errors marred the introduction of one of the first computerised vote counting systems to be used in the UK.
The errors almost derailed a trial of the system of electronic vote counting, which will be used for the London mayor and Greater London Assembly elections in May.
Greater London returning officer Robert Hughes and DRS Data & Research Services, which has been contracted to count the vote, organised a trial involving 1.6 million papers from more than 500 ballots.
However, confusion over the number of ballot papers used delayed the start of counting at Hammersmith Town Hall for one hour.
Once underway, DRS staff monitored a set of 12 scanners that read two ballot papers a second.
Hughes said: "It is important that we test the process fully before deciding whether or not to go ahead with it on 4 May.
"We based this rehearsal on a 60% turnout. My staff made sure that there are a reasonable number of spoilt papers, folded papers and votes of questionable validity, so the trial is as realistic as possible."
DRS will provide its own DRS CD800 scanners and bespoke software to 14 counting centres across London, in a £1.7m leasing deal.
Tony Lee, DRS technical director, claimed traditional vote counting in the highly complex London elections would take three days, but DRS would deliver the result by the next morning.
The Home Office is also running electronic voting and counting trials in six local authorities outside the capital, as part of an effort to boost election turnout rates.
Bury hopes to trial both electronic voting and counting using touch screen computers in one ward.
Broxbourne and Three Rivers councils intend to use electronic counting, while Salford and Warrington will use electronic voting.
Nick Easton, head of policy at the Local Government Association, said, "We are very keen on these developments.
"We hope they will make a difference," he added.
John Turner, chairman of the Association of Electoral Administrators, said it was inevitable that electronic voting would spread, but said, "We need robust systems."
"We have got to satisfy candidates that the result is what voters voted for and convince the electorate that their votes cannot be traced back to them," he added.