That’s a Teddington control. Not a easy calibrator. Check for the bulb and cap tubing to be properly mounted, and not crimped or crushed before even attempting any change. They are not like a BJ and do float with load. If off 50 degrees or more, just replace it. They do drift from off to on burner a considerable amount. Make sure to place a load in when testing. Hotel pan 1/2 full of water works well.