e., when
the balance is performing with an arc (or motion) of 11/4 revolutions
or 225 degrees each way from a point of rest. Under such conditions the
actual contact will not take place before some little time after the
impulse jewel has passed the five-degree arc between the lines _c e_ and
_c g_.
THE DROP AND DRAW CONSIDERED.
Exactly how much drop must be allowed from the time the tooth leaves the
impulse jewel before the locking tooth engages the locking jewel will
depend in a great measure on the perfection of workmanship, but should
in no instance be more than what is absolutely required to make the
escapement safe. The amount of draw given to the locking stone _c_ is
usually about twelve degrees to the radial line _k a_. Much of the
perfection of the chronometer escapement will always depend on the skill
of the escapement adjuster and not on the mechanical perfection of the
parts.
The jewels all have to be set by hand after they are made, and the
distance to which the impulse jewel protrudes beyond the periphery of
the impulse roller is entirely a matter for hand and eye, but should
never exceed 2/1000".
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