If you notice any instability in your gimbal, you will want to do some calibrating. Before you do a motor calibration, you always want to first try the six point calibration as that will usually fix any issues you are having with the stability of the gimbal. However, if it doesn't resolve your issue you can do a motor calibration.
A motor calibration will allow you to adjust the leveling of the tilt and roll motor.
You will want to adjust the values until you see your gimbal is leveled so there is no set of values required. However, you will not see any changes in the gimbal as you adjust the values until you first click the "check mark", then click "save".