Over the limit is far from being drunk as far as I know, so there is no way to assess if you are just over or under the limit.
Oh please. You are meant to abstain for 8 hours. If you are still over the limit 8 hours after you stopped drinking you must have had quite a lot. It's much easier to tell your alcohol state at the start of those 8 hours rather than at the end of them!
According to info on the web...
Typically in 8 hours a normal person should metabolise the equivalent of about 8 "drinks" where a drink is either:
a) 12oz bottle beer
b) 4oz of wine
c) 1oz of 80% proof
Are you saying you aren't aware of feeling "altered" after drinking 8 beers and need a machine to tell you?