Abstract: A method and apparatus for endpoint detection is provided. Endpoint is determined by monitoring throttle valve position during a production instance of a given process, and by comparing a production signal obtained thereby with a calibration signal previously obtained by monitoring throttle valve position during performance of the process on a chamber or on a wafer of known constitution. The production process endpoint may be set based on the endpoint time of the calibration signal, or may be determined by filtering the calibration signal and the production signal to identify features thereof and by comparing the pattern of features of the production signal with the pattern of features of the calibration signal. Preferably throttle valve positions are filtered using a low pass finite impulse response filter of order three.