Watches that have below standard train gearings require considerably stronger mainsprings than do those which have correct gearing and they will seldom take a reasonably good motion without a strong spring.
A safe way to judge gearings if in doubt is by the motion and the engaging surfaces of the wheel teeth. If the motion is steady and the teeth are not cut by the pinion leaves they may be considered as satisfactory. If the motion is steady for a time and then suddenly drops off there is generally something wrong in the gearing. The wheel and pinion in error can be determined by noting at what particular intervals the motion decreases. In nearly all instances this condition will cause a gaining rate in the vertical positions because of the fact that the vertical arcs are shorter and comparatively more easily affected than the horizontal arcs.
CHAPTER XV
TIMING AND FINAL REGULATION
[75.]Mean Time Screws and Timing Washers.
In the general overhauling of watches, changing staffs, retruing and repoising of balances it is often necessary to make corrections of several minutes per day in the mean time.
For this reason and for the convenience of the future some manufacturers have provided from two to four mean time screws in the balances. A complete revolution of these screws either in or out, generally corrects any variation that may be required and frequently considerably less is all that is required in bringing the watch to time.
It is of course necessary that these screws be turned in opposite pairs as well as equal distances and that they be fitted with enough friction to prevent looseness and not too tight to cause bending of the pivots when they are turned.
If properly used for the purpose for which they were intended they are of inestimable value to the repairing fraternity in producing results.