Proper tuning of a controller is not only essential to its correct operation but will also greatly improve product quality, reduce scrap, shorten down-time and save money. Procedures for tuning conventional PID controllers are well established and simple to perform. Any time a controller is replaced, the new instrument must be retuned, which can be difficult under certain running conditions. Some controllers have digital settings for the three control parameters: Proportional Band, Integral time constant and Derivative time constant. This feature makes it simple to reproduce the correct parameter settings when replacing an instrument but does not help if heaters are changed or the mechanics of the system are altered appreciably. In this instance the associated controller must be "re-tuned" to insure optimal performance.