Given a reasonable amount of time and a system that exercises the control loop with setpoint changes and load disturbances, PRAC+ tunes the PID to very near optimal values. If control seems poor even after several days, the loop to which you are applying the PID may be one for which PRAC+ does not tune well. If PRAC+ is unable to tune, the problem often lies in a misapplication of the algorithm or a poorly designed HVAC system.