1. A method of deriving operating characteristics for a process tool used for processing workpieces the method being performed with a sensor apparatus having a plurality of detectors, the method comprising the steps of: a) loading a sensor apparatus including electronic devices into the process tool; b) measuring the operating characteristics with the sensor apparatus; c) converting the measured operating characteristics into digital data; d) deriving correction factors for the measurements; and e) applying the correction factors to the measured data so as to generate corrected data.