R13...
Honorary Master
Not in all cases - like on the cusp.
http://en.wikipedia.org/wiki/Breathalyzer
Research indicates that breath tests can vary at least 15% from actual blood alcohol concentration[citation needed]. An estimated 23% of individuals tested will have a BAC reading higher than their true BAC[citation needed]. Police in Victoria, Australia, use breathalyzers that give a recognized 20% tolerance on readings. Noel Ashby, former Victoria Police Assistant Commissioner (Traffic & Transport), claims that this tolerance is to allow for different body types
Things like breathing patterns can even effect reading. Is it fair to lock away people to rot in jail?
Such things by their nature are meant to cover a majority of cases. It would be expensive and unreasonable to treat every case on its own merit at the side of the road which is why they take a blood sample and allow you to individualize your case in front of a judge who by the way is also bound to be subjective but within reason.