Going wildly off topic here, but the legal limit for alcohol levels is set by s11 of the Road Traffic Act 1988, which says
'the prescribed limit ' means, as the case may require :-
(a) 35 microgrammes of alcohol in 100 millilitres of breath,
(b) 80 milligrammes of alcohol in 100 millilitres of blood, or
(c) 107 milligrammes of alcohol in 100 millilitres of urine,
or such other proportion as may be prescribed by regulations made by the Secretary of State.