Abstract: A system and method which implements a preferred embodiment of the present invention detects the endpoint of a process by monitoring changes in chamber pressure in real time. The endpoint of a process may be detected for processes that produce measurable changes in chamber pressure. For example, chemical reactions conducted within the chamber, such as during a cleaning process, may result in changes to chamber pressure. As the chamber is cleaned, the chamber pressure is maintained using an evacuation conductance modulating device, such as a throttle valve, to prevent gaseous by-products of the cleaning process from changing the chamber pressure. As the cleaning process progresses, less contaminants exist and less by-product evolves. As a result, if the throttle valve position is held constant, then variables, such as a decrease in the rate of change in chamber pressure, can be used to detect the endpoint of the process.