When I worked in science labs it always made me think about where you stop with calibration of equipment. Ok so depending on how critical the measurement was the piece of kit was making, usually denoted how often and to what tolerances, the piece of kit needed to be calibrated to. So a piece of kit making a critical measurement like a HPLC (high pressure liquid chromatography) which have the result for the active ingredient percentage (w/v) in a pharmaceutical product would need calibration by the laboratory every morning before use for the day by running standards made by an external company. Then every 3 months an external engineer would have to calibrate the kit using a piece of kit he has that is calibrated by a national standard laboratory. Now this is where it gets a bit much. The kit the national standard lab uses to calibrate the calibration engineers kit, guess what, needs calibrating monthly by having an engineer from the standards laboratory calibrate his kit. My dilemma always was where do you stop? When the kit doing the calibration becomes the one that can’t be calibrated , what then? What happens. To this piece of kit, is it just taken as gospel that this piece of kit will never need to be calibrated?