A
square ruby pin requires more shake than any other kind; it enters the fork and receives the impulse in a diagonal direction on the jewel, in which position it is illustrated at
Z
, [Fig. 20]. This ruby pin acts on a knife edge, but for all that the engaging friction during the unlocking action is considerable.
Our reasoning tells us it matters not if a ruby pin be wide or narrow, it must have the same freedom in passing the acting edge of the fork, therefore, to have the impulse radius on the point of intersection of
A′X
with
AW
, [Fig. 17], we would require a very narrow ruby pin. With 1° of freedom at the edge, and ½° in the slot, we could only have a ruby pin of a width of 1½°. Applying it to the preceding example it would only have an actual width of .0785 × 1.5 = .1178 mm., or the size of an ordinary balance pivot. At
n