Exactly, there is quite a bit of news stories every year about "here is how many drinks a person of this height and weight can have before being .08" or whateve

Exactly, there is quite a bit of news stories every year about "here is how many drinks a person of this height and weight can have before being .08" or whatever. Just don't drink and drive, that's the only sure fire way to not get accused. Especially for a limit you can't test yourself without spending ~$100USD to get a personal tester which they don't guarantee the accuracy of. We're trying to enforce laws on an uneven playing ground (a limit the average citizen can't test against until it's too late).