there not accurate for the 15 minutes I believe It is after the drink, that's the court standard atleast. that's why the officer will usually ask when you had your last drink then wait if necessary.I had a friend who had a calibrated breathalyzer made by the same company that makes the popo units. I drank two 0.5L beers, and few mins after I finished the second one I blew 0.05.
.