This fault produces a
scraping sound in a watch. Suppose we attempt to remedy the fault by
bending forward the guard pin _b_, as indicated by the dotted outline
_b'_ in Fig. 103, said figure being a side view of Fig. 102 seen in the
direction of the arrow _a_. This policy would prevent the engaged pallet
from passing off of the locking face of the pallet, but would be
followed by the jewel pin not passing fully into the fork, but striking
the inside face of the prong of the fork at about the point indicated by
the dotted line _m_. We can see that if the prong of the fork was
extended to about the length indicated by the outline at _c_, the action
would be as it should be.
To practically investigate this matter to the best advantage, we need
some arrangement by which we can determine the angular motion of the
lever and also of the roller and escape wheel. To do this, we provide
ourselves with a device which has already been described, but of smaller
size, for measuring fork and pallet action.
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