the guy who actually drank, they should have tested him right after that last shot and then later on as well, to show the difference between the alcohol in the mouth and the alcohol that is coming from the deep lung air (which shows what's actually in the blood.) there's a reason the police will only test after 15 or 20 minutes (depending on state) of observation so that anything in the mouth if they just had a drink or did use mouthwash or something would not affect the results.
So it's not inaccurate, you just haven't followed the instructions...? It makes sense, it gives time for any thing you've put in your month to be ingested/no longer in your mouth. It's not inaccurate, if you want to see what'll you've get if you get pulled over, obviously don't wait 20 minutes. If you want to know your blood alcohol (obviously, its not a blood test, so not AS accurate as literally testing blood), breathalysers are to get an idea of where your BAC is. In Australia who use these as the primary test, you are taken back to the station and given the 20 minutes if it hasn't already been and you're tested on a proper machine. Far more accurate than what the US does with their walking on the line tests lol.
