We can readily see that as we increase the height of the heel of the
impulse face of our tooth we must also increase the angle of impulse
imparted to the cylinder. With the advantages of accurate micrometer
calipers now possessed by the horological student it is an easy matter
to get at the angular extent of the real lift of any cylinder. The
advantage of such measuring instruments is also made manifest in
determining when the proper proportion of the cylinder is cut away for
the half shell.
[Illustration: Fig. 130]
In the older methods of watchmaking it was a very common rule to say,
let the height of the incline of the tooth be one-seventh of the outer
diameter of the cylinder, and at the same time the trade was furnished
with no tools except a clumsy douzieme gage; but with micrometer
calipers which read to one-thousandths of an inch such rules can be
definitely carried into effect and not left to guess work. Let us
compare the old method with the new: Suppose we have a new cylinder to
put in; we have the old escape wheel, but the former cylinder is gone.
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