This will be understood by
inspecting Fig. 137, which is a vertical longitudinal section of a
chronometer balance staff, the lower side of the impulse roller being
cupped out at _c_ with a ball grinder and finished a ball polish.
[Illustration: Fig. 136]
[Illustration: Fig. 137]
It will be seen the impulse roller is staked flat against the hub _E_ of
the balance staff. The unlocking roller, or, as it is also called, the
discharging roller, _C_, is usually thinner than the impulse roller and
has a jewel similar to the impulse jewel _a_ shown at _f_. This roller
is fitted by friction to the lower part of the balance staff and for
additional security has a pipe or short socket _e_ which embraces the
balance staff at _g_. The pipe _e_ is usually flattened on opposite
sides to admit of employing a special wrench for turning the discharging
roller in adjusting the jewel for opening the escapement at the proper
instant to permit the escape wheel to act on the impulse jewel _a_.
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