DC motor speed calibration

[XaviPacheco]

I have seen some treadmills with DC motors that have an option in the console to calibrate the speed sensor by making the motor run from 0 to max speed. Also, some of them have an external potentiometer to compensate torque. When is this calibration needed, or under what condition the system loses calibration?

I have designed my own motor controller for this kind of motors, and I used a PI controller microcontroller-based to compute the duty cycle according to the setpoint given. It works well even if the load varies. Do I need to add a calibration option as well? Let's say I use my motor controller with different DC motors ranging from 1 to 4HP. Or let's say I change my speed sensor, and now I have more pulses per revolution than before. I think the system characteristics would vary, right? Is here when calibration comes to play? Maybe I'm using better technology that those old motor controllers and I don't need this?