of 28°. At the intersection of this angle with the fork angle
k
A′
m
, we draw
i i
from the center
A
; this gives us the theoretical impulse circle. The total lock being 1¾° it follows that the angle described by the balance in unlocking = 1¾ × 2.7316 = 4.788°. According to the specifications the width of slot is to be 5⅛°; placing the center of the protractor on
A