The "Pen" models correspond to the standard measurement of ATP. The A3 models are based on a new technology that determines not only ATP (adenosine triphosphate) but also the lower energy molecules ADP (adenosine diphosphate) and AMP (adenosine monophosphate). A considerable advantage when controlling hygiene in food processing areas involving heating, fermentation, etc. Indeed, ATP is degraded into ADP and AMP during these processes, the presence of which is undetectable with usual ATP measurements, although they can be a source of contamination. Testing with A3 tests is now strongly recommended (at no additional cost compared to ATP).