This condition is more critical in higher grade watches. Therefore the correct greases should be used. Checking for creep is much easier if you work on the same calibre's, by keeping dummy barrel covers with inspection holes. Hold the barrel arbor in barrel tongs and holding the barrel wind the spring to the top and hold it still . Observe the spring through the inspection holes for a few moments and check for creep.
Some barrels have scallops cut in the barrel wall to prevent the mainspring creeping down.
Or shortening the bridle by 0.5 mm. and squaring the end of the spring should prevent slipping. After making any alterations to the spring it is advisable to check the completed watch for amplitude, half wound, and fully wound this exceeds 320 Deg. and 310 Deg. respecavly then fit a weaker spring. If the amplitude is low half wound and too high full wound then the bridle may be griping the barrel wall too much. We welcome your comments and suggestions. Upton Hall, Upton, Newark, Notts.