https://www.google.com/amp/s/www.q13fox.com/news/kitsap-judges-ruling-could-eventually-invalidate-tens-of-thousands-dui-convictions-statewide.amp

Because cops are too stupid to round.

Note: This is not a cops specific stupidity. I've encountered many people who do not know how to round.

But in this case, the state law specifies a certain procedure that the software did not follow and it presented too many levels of accuracy to the human to interpret.

The software displays too many digits to the right of the decimal place. There is a particular rule it should have followed. It didn't. It forced the cop to fill out a form that allowed for three decimal places and there were stated rules on truncating at the 4th and rounding at the third that the cop would have to do at that point in his head. Which I assume the cops have been doing forever.

But that leaves an opening in court to challenge the cops ability to round and do math instead of merely copying the known output from a device.