club-tooth lever escapement with equidistant locking, we
commence, as on former occasions, by producing the vertical line _A k_,
Fig. 22, and establishing the center of the escape wheel at _A_, and
with the dividers set at 5" sweep the pitch circle _a_. On each side of
the intersection of the vertical line _A k_ with the arc _a_ we set off
thirty degrees on said arc, and through the points so established draw
the radial lines _A b_ and _A c_.

From the intersection of the radial line _A b_ with the arc _a_ lay off
three and a half degrees to the left of said intersection on the arc
_a_, and through the point so established draw the radial line _A e_.
From the intersection of the radial line _A b_ with the arc _a_ erect
the perpendicular line _f_, and at the crossing or intersection of said
line with the vertical line _A k_ establish the center of the pallet
staff, as indicated by the small circle _B_. From _B_ as a center sweep
the short arc _l_ with a 5" radius; and from the intersection of the
radial line _A b_ with the arc _a_ continue the line _f_ until it
crosses the short arc _l_, as shown at _f'_. Lay off one and a half
degrees on the arc _l_ below its intersection with the line _f'_, and
from _B_ as a center draw the line _B_ _i_ through said intersection.
From _B_ as a center, through the intersection of the radial line _A b_
and the arc _a_, sweep the arc _g_.

The space between the lines _B f'_ and _B i_ on the arc _g_ defines the
extent of the locking face of the entrance pallet _C_. The intersection
of the line _B f'_ with the arc _g_ we denominate the point _o_, and
from this point as a center sweep the short arc _p_ with a 5" radius;
and on this arc, from its intersection with the radial line _A b_, lay
off twelve degrees, and through the point so established, from _o_ as a
center, draw the radial line _o m_, said line defining the locking face
of the entrance pallet _C_.

[Illustration: Fig. 22]

It will be seen that this gives a positive "draw" of twelve degrees to
the entrance pallet; that is, counting to the line _B f'_. In this
escapement as delineated there is perfect tangential locking. If the
locking face of the entrance-pallet stone at _C_ was made to conform to
the radial line _A b_, the lock of the tooth _D_ at _o_ would be "dead";
that is, absolutely neutral. The tooth _D_ would press the pallet _C_ in
the direction of the arrow _x_, toward the center of the pallet staff
_B_, with no tend