MATH(PID channel, setpoint!, measurement))

This function must be called in the PID callback subroutine for the channel specified and returns the output of the controller function.

The setpoint value is the desired state that the controller is trying to achieve.

The measurement is the current value of the real world.

https://www.thebackshed.com/forum/ViewTopic.php?FID=16&TID=17263 For an example of setting up and running a PID controller