Sew - as soon as a methodology for doing the bkg. subtract is established, full speed ahead. The 30day +/- 20% buildup factor will have to be accounted for, especially in legal states, if the constabulary is to truly determine if a person is operating under the influence. That with the SME live time, curbside analysis by the DRE(drug recognition expert) who took and extra week of class at the local technical college to attain said designation. With current events being where they are, and the full eclipse of civil chaos looming dangerously close, and with the ensuing governmental response , keep a watchful eye on all things within the civil liberties arena. Todays HP trivia - shielding buildup is just a fancy term for Comptons scattering within a high Z type shielding matrix - Pb would be the basis material.
