With reference to the escapement, good watchmakers often have different methods of examining the various points and of making corrections and it is not of so much importance as to just how correct conditions are obtained, as it is that they actually be obtained.
Whatever the method may be it is certain that each escape wheel tooth must have positive locking on each pallet stone and that there must be positive space for drop between the back of each stone and the pointed end of each escape wheel tooth. There must also be sufficient draw when each tooth and stone are locked to hold the fork against the bankings.
When the lock, drop and draw are correct it is next necessary to see that the fork length and guard pin freedom are correct.
There is only one positive method of determining as to when the fork length is correct, and this is through closing the bankings to drop.
This can be done either before or after placing the balance in the watch and merely requires turning the banking screws so that the excentric pins will close in on the fork until the fork arrives at the pins, at the same instant that the tooth drops on the pallet stone. This eliminates any slide of the stone on the tooth beyond the actual locking and in this condition it is required that the roller jewel pass through the fork slot and out of the fork horn entirely on both sides with perfect freedom.
Should it touch on both sides of the fork, then the fork is either too long or the roller jewel is too far forward, and if it touches on one side only it may require simply equalization of the freedom. The guard pin length also must be obtained with the bankings closed to drop and should be just free from the safety roller on both sides.
When the inspection proves that these conditions have been properly provided for, it is necessary to slightly open the bankings so that there will be just a trifle of slide of each stone, on each tooth, after the locking takes place.
Extremely wide side shakes of the escape, pallet or balance pivots will sometimes cause striking of the roller jewel when conditions are otherwise correct, and these side shakes should not be very much beyond the extreme limits mentioned in this number. The fact of this feature, however, should not be construed as a recommendation that these pivots be closely fitted, for reasonable freedom is to be desired because it is positively necessary.