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Saw the program.....I would have assumed the following. Every measuring machine in the world has to have a level of tolerance. If you did Physics in college people start taking about something being X metres +/- 2% or whatever.
Therefore, if that machine has a tolerance reading of 10% than that reading was 42 +/- 4.2. I.e. Maybe he was under the reading if the machine was more accurate. I think its the same principle as to why the guards don't clock you for goign 61 in a 60 zone. Maybe even though their machine says 61, your speedometer says 60 etc etc.
In addition, both the checks on your man were breath checks. I would presume it is his right to demand that a blood check, which is the proper proper measurement I would assume(as the limit is in terms of alcohol in your blood) that he had the right to demand to take a blood sample text.
If the doctor took 20 minutes to get there, and lets be honest it would probably take longer, and your man swamped himself with water for that 20 minutes he'd pull himself back under the limit.
The scam I have heard of is that you demand for the doctor etc etc, put your head in a trough and start drinking water and then when he arrives profess to a fear of needles and go with the urine sample and hope you have diluted it.
As I never ever ever even take a sip of a drink if driving I can't comment on how it works or not works....I could never drink and drive anyways. For starters when I'm drunk I often think that if I was in a car I'd hit the first parked car in sight....I have no idea how you would steer when drunk. And second,I'd never be able to sleep again if I blew someone into pieces because I was drunk at the wheel.