Quality control has the responsibility for calibrating VLT instruments and quantitatively assessing the quality of data. The main classes are QucCalibrationPlan, QucCalibrationData, QucEquipmentModel, QucReductionRecipes and QucReductionRules.

The calibration plan defines the observation, calibration procedures and data needed to achieve the specified quality level defined by Instrument Scientist. It creates technical programs and verifies the data archived in the calibration database. For this purpose it can invoke an equipment model providing reference values of exposure and simulated observations. Quality control and trend analysis reports are generated.

A concept inherent to quality control is the distributed system: it allows several on-line users to simultaneously do some analytical processing of distributed data, since it performs in a distributed environment.