Abstract: A method by which a user can modify or interact with a computer controlled measurement process at one or more specified points within the code controlling the process. These points are called variation points and are inserted by the designer at points in the code where a designer anticipates that a user may want to interact with or modify the process. In operation, when a variation point is reached, control passes to a user-defined process or subsystem. The user-defined subsystem performs one or more actions, including modification of measurement data, control of a device being tested and variation of numerical and control parameters defining the measurement process. Control may then be passed back to the measurement process. Subsequent operations performed by the measurement process may be affected through the numerical and control parameters.