Note from the editors: On November 21, 2013 we discovered the post below did not follow our standard practice for attribution, which is to quote and link to original sources. The source in question is The OC Register. The editor responsible is no longer working for LAist, and we are reviewing each of her other posts and will issue corrections if we discover any other errors.

For about five months this year, a flawed test at the Orange County Crime Lab has been churning out inaccurate blood-alcohol readings that became part of hundreds of criminal drunk driving cases.

About 20 people have been wrongly identified as driving with blood-alcohol levels above the legal limit of .08 when they were really just below it, the Orange County Register reports.

"The Orange County District Attorney’s Office sent letters this month to 900 people who have been convicted or pleaded guilty in cases that involved the flawed readings. The letters advise them to talk to an attorney “if you have any questions regarding the legal significance” of the error. About 1,300 cases remain open."

The errors began in late May, when the crime lab calibrated one of the machines it uses to analyze blood samples but didn’t save one data point in the software, according to the Register. That threw off the machine by .003 percentage points, which is enough to cause a problem.

But that doesn't mean drivers who had the wrong blood-alcohol levels posted are off the hook. Blood draws don’t always at the moment of a drunken-driving stop, and .07 in the lab could have been .09 on the highway.

“We go to trial on .07 DUIs quite frequently,” Senior Assistant District Attorney Mary Anne McCauley told the Register. “And we win convictions.”

Defense attorneys say the error raises questions about the lab's credibility, and that could help their cases — even if it doesn't change their clients' test results.