the nature of a fault, but whenever there are two faults we
must choose the less. The rate of the watch will suffer less on account
of the recoil introduced than it would were the locking faces arcs of
circles struck from the pallet center, in which case the guard point
would often remain against the roller. The draw should be as light as
possible consistent with safety of action; some writers allow 15deg. on the
engaging and 12deg. on the disengaging pallet; others again allow 12deg. on
each, which we deem sufficient. The draw is measured from the locking
edges M and N, Fig. 5. The locking planes _when locked_ are inclined 12deg.
from EB, and FB. In the case of the engaging pallet it inclines toward
the center A. The draw is produced on account of MA being longer than
RA, consequently, when power is applied to the scape tooth S, the pallet
is drawn into the wheel. The disengaging pallet inclines in the same
direction but away from the center A; the reason is obvious from the
former explanation. Some people imagine that the greater the incline on
the locking edge of the escape teeth, the stronger the draw would be.
This is not the case, but it is certainly necessary that the point of
the tooth alone should touch the pallet. From this it follows that the
angle on the teeth must be greater than on the pallets; examine the
disengaging pallet in Fig. 5, as it is from this pallet that the
inclination of the teeth must be determined, as in the case of the
engaging pallet the motion is toward the line of centers AB, and
therefore _away_ from the tooth, which partially explains why some
people advocate 15deg. draw for this pallet. As illustrated in the case of
the disengaging pallet, however, the motion is also towards the line of
centers AB, and _towards_ the tooth as well, all of which will be seen
by the dotted circles MM2 and NN2, representing the paths of the
pallets. It will be noticed that UNF and BNB are opposite and equal
angles of 12deg. For practical reasons, from a manufacturing standpoint,
the angle on the tooth is made just twice the amount, namely 24deg.; we
could make it a little less or a little more. If we made it less than
20deg. too great a surface would be in contact with the jewel, involving
greater friction in unlocking and an inefficient draw, but in the case
of an English lever with such an arrangement we could do with less
drop, which advantage would be too dearly bought; or if the angle is
made over 28d