The Quality Assurance Test is our final factory test which is a verification of the calibration, but not a calibration. The unit cannot be calibrated; there are no adjustments. We verify it to tighter specs than the published specifications. The verification is only done at one temperature and humidity point, in a stable environment, against a traceable, calibrated laboratory measurement probe. The APC probe is not intended to be a laboratory instrument, it is designed to be adequate for the environmental management of a data center, computer room, wiring closet, etc.