Inhave several police officer friends and after comparing it is fairly close within .01 tolerance of professional units.i would definitely not operate a car if it registered anything close to .06 given its accuracy. It is more accurate with fresh batteries and if you follow use instructions by waiting 20 minutes after last consumption of any liquid or food including alcohol before testing levels as particle contamination in mouth will alter results. Please remember even if you're below the legal limit you may still be impaired. I was very surprised to discover how intoxicated. 08 actually is