Originally Posted by bpe

The systems are probably based on the same technology as used in other countries and in military applications (Ion mobility spectrometry if anyone is interested; NMR is much much less sensitive) as very few other techniques can give results within seconds. Adjusting the sensitivity or at least the threshold of a 'positive' would be possible, but just as important as that is the calibration, which tells the instrument what to look for, and accuracy may drift over time if done improperly or not often enough.

The image from OP only lists 'time', which just matches something in the calibration so it's not possible to tell what it is. False positives (of similar or entirely unrelated chemicals) are possible, although the system would be designed to avoid or at least know common ones if calibrated and operated properly.