The Minnesota Supreme Court is scheduled to hear a case involving the accuracy of a device that measures blood-alcohol levels in people who have been accused of driving under the influence (DUI).

According to The New York Times, about 4,000 people in the state have challenged the results of the breath-testing device used by law enforcement agencies. The state says the test results are correct, and can be used to punish people who are found to be driving with alcohol levels that are above the legal limit of .08.

A state judge this year ruled that while the source code for the device, called the Intoxilyzer 5000EN, had errors, this did not affect the results’ accuracy. That decision was appealed.

Ryan Pacyga, a lawyer who represents almost 200 people accused of DUI, and who are now challenging the results, told the newspaper the more air a person blows into the machine, the higher the alcohol rate it registers. He pointed out that officers often tell people to blow harder into the machine. The state and the device’s manufacturer both say blowing harder into the machine does not result in a higher blood-alcohol level, the article notes.