tally votes. The paper it prints is the official ballot, put into a scanning system which counts the barcodes, or the printed names can be hand-counted, as a check on the machines. Most voters do not look at the paper to ensure it reflects their choices, and when there is a mistake, an experiment found that 81% of registered voters do not report errors to poll workers. Two companies, Hart and Clear Ballot, have scanners which count the printed names, which voters had a chance to check, rather than bar codes and QR codes, which voters are unable to check. Timing of optical scans The machines are faster than hand-counting, so are typically used the night after the election, to give quick results. The paper ballots and electronic memories still need to be stored, to check that the images are correct, and to be available for court challenges. Errors in optical scans Scanners have a row of photo-sensors which the paper passes by, and they record light and dark pixels from the ballot. A black streak results when a scratch or paper dust causes a sensor to record black continuously. A white streak can result when a sensor fails. In the right place, such lines can indicate a vote for every candidate or no votes for anyone. Some offices blow compressed air over the scanners after every 200 ballots to remove dust. Fold lines in the wrong places can also count as votes. Software can miscount; if it miscounts drastically enough, people notice and check. Staff rarely can say who caused an error, so they do not know whether it was accidental or a hack. Errors from 2002-2008 were listed and analyzed by the Brennan Center in 2010. There have been numerous examples before and since. In a 2020 election in Baltimore, Maryland, the private company which printed ballots shifted the location of some candidates on some ballots up one line, so the scanner looked in the wrong places on the paper and reported the wrong numbers. It was caught because a popular incumbent got implausibly few votes. In a 2018 New York City election when the air was humid, ballots jammed in the scanner, or multiple ballots went through a scanner at once, hiding all but one. In a 2000 Bernalillo County (Albuquerque area), New Mexico, election, a programming error meant that straight-party votes on paper ballots were not