As an illustration, let us consider the subject of depth between the
cylinder and the escape wheel. As previously stated, 196 degrees of
cylinder shell should be employed; but suppose we find a watch in which
the half shell has had too much cut away, so the tooth on entering the
half shell after parting with the entrance lip does not strike dead on
the inside of the shell, but encounters the edge of the exit lip. In
this case the impulse of the balance would cause the tooth to slightly
retrograde and the watch would go but would lack a good motion. In such
an instance a very slight advance of the chariot would remedy the
fault--not perfectly remedy it, but patch up, so to speak--and the watch
would run.
[Illustration: Fig. 135]
In this day, fine cylinder watches are not made, and only the common
kind are met with, and for this reason the student should familiarize
himself with all the imaginary faults which could occur from bad
construction. The best way to do this is to delineate what he (the
student) knows to be a faulty escapement, as, for instance, a cylinder
in which too much of the half shell is cut away; but in every instance
let the tooth be of the correct form.
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