76]
We can also make use of our angle-testing device for measuring our
escape-wheel action, by letting the clasp embrace the arbor of the
escape wheel, instead of the pallet staff. We set the index arc as in
our former experiments, except we place the movable index _D_, Fig. 76,
so that when the engaged tooth rests on the locking face of a pallet,
the index hand stands at the extreme end of our arc of twelve degrees.
We next, with our pointed pegwood, start to move the fork away from the
bank, as before, we look sharp and see the index hand move backward a
little, indicating the "draw" on the locking face. As soon as the pallet
reaches the impulse face, the hand _A_ moves rapidly forward, and if the
escapement is of the club-tooth order and closely matched, the hand _A_
will pass over ten and a half degrees of angular motion before the drop
takes place.
[Illustration: Fig. 77]
We will warn our readers in advance, that if they make such a testing
device they will be astonished at the inaccuracy which they will find in
the escapements of so-called fine watches.
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