PID parameters are unique for each specific system. They depend on the hardware of the system. Auto-tune is an independent module. When started, it performs a few On-Off cycles. It then learns the overshoot/undershoot “waves” and, according to their “dimensions”, sets PID parameters. It’s recommended to perform Auto-tune only once – when building and tuning the system. Then it can run for years with these parameters. In some cases, it’s recommended to perform Auto-tune on setpoint, about 10% lower than the real one.