The bridge _F G_ carries the top pivots of
escape wheel and pallet staff, and is shaped as shown at the full
outline. This bridge is supported on two pillars 1/2" high and 1/2" in
diameter, one of which is shown at _E_, Fig. 25, and both at the dotted
circles _E E'_, Fig. 24.
To lay out the lower plate we draw the line _a a_ so it passes through
the center of _A_ at _m_. At 1.3" from one edge of _A_ we establish on
the line _a_ the point _d_, which locates the center of the escape
wheel. On the same line _a_ at 1.15" from _d_ we establish the point
_b_, which represents the center of the pallet staff. At the distance of
1.16" from _b_ we establish the point _c_, which represents the center
of the balance staff. To locate the pillars _H_, which support the top
plate _C_, we set the dividers at 2.58", and from the center _m_ sweep
the arc _n_.
From the intersection of this arc with the line _a_ (at _r_) we lay off
on said arc _n_ 2.1" and establish the points _g g'_, which locate the
center of the pillars _H H_.
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