In actual fact, the balance at the time the unlocking
takes place is moving with nearly its greatest peripheral velocity and,
as stated above, the escape wheel is at rest.
Here comes a very delicate problem as regards setting the unlocking or
discharging jewel. Let us first suppose we set the discharging jewel so
the locking jewel frees its tooth at the exact instant the impulse jewel
is inside the periphery of the escape wheel. As just stated, the escape
wheel is not only dead but actually moving back at the time the release
takes place. Now, it is evident that the escape wheel requires an
appreciable time to move forward and attack the impulse jewel, and
during this appreciable time the impulse jewel has been moving forward
inside of the arc _A A_, which represents the periphery of the escape
wheel. The proper consideration of this problem is of more importance in
chronometer making than we might at first thought have imagined,
consequently, we shall dwell upon it at some length.
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