G H
, the primitive or geometrical circle of the escape wheel; set the center of the protractor at
B
and mark off an angle of 30° on each side of the line of centers; this will give us the angles
A B E
and
A B F
together, forming the angle
F B E
of 60°, which represents from lock to lock of the pallets. Since the chord of the angle of 60° is equal to the radius of the circle, this gives us an easy means of verifying this angle by placing the compass at the points of intersection of