What is the term used for the departure of the control point from the set point?

The term for the departure of the control point from the set point is "Deviation." In the context of control systems and instrumentation, deviation refers specifically to the difference between the desired set point (the target value you want to maintain) and the actual value measured by the control system. This is a critical concept in process control, as it helps operators understand how far the system is from its target and allows for appropriate corrective actions to be taken.

By measuring deviation, control systems can adjust inputs to bring the process variable back to the set point, ensuring optimal performance and efficiency. Understanding deviation is essential for maintaining stability in systems and for troubleshooting when variables do not behave as expected.