To come back to the impulse angle, some might use a proportion of 3.5, 4 or even 5 to 1, while others for the finest of watches would only use 2.75 to 1. By having a total vibration of the balance of 1½ turns, which is equal to 540° a fork angle of 10° and a proportion of 2.75 for the impulse angle which would be equal to 10 × 2.75 = 27.5°. The free vibration of the balance, or as this is called, “the supplemental arc,” is equal to 540° − 27.5° = 512.50°, while with a proportion of 5 to 1, making an impulse angle of 50°, it would be equal to 490°. To sum up, the finer the watch the lower the proportion, the closer the action to the line of centers, the smaller the friction. On account of leverage the more difficult the unlocking but the more energetic the impulse when it does occur. The velocity of the ruby pin at
P
; [Fig. 14], is much greater than at
W
, consequently it will not be overtaken as soon by the fork as at
W
. The velocity of the fork at the latter point is greater than at
P
; the intersection of
ii