Staff Gauge
The tool shown in Figs. 145 and 146, the invention of Mr. E. Beeton, is designed for measuring the height of the balance staff from the balance seat to the end of the top pivot. Fig. 146 is enlarged to give more distinctness.
E E' is a piece of curved steel about 1/20 of an inch thick, and 1/15 of an inch wide. On the lower side of E' to the end the arm is filed down in width and thickness to correspond to an ordinary balance arm; C is a slot in the upper arm E, which allows A, B, D, A' to be moved backward and forward. D D' is a round brass post drilled and tapped, the part D' has a thread cut on it, and the part shown in the slot C fits with easy friction. B is a lock-nut, drilled and tapped to fit the thread on D'. It is for the purpose of clamping D D' against the arm E. A A' is a small steel screw with milled head, and is made to fit the tapped hole in D D'.
Mr. Beeton describes his method of using this tool as follows: Take your measurement of the distance the balance seat is to be from end of the top pivot, as follows: remove the end stone in balance cock, and screw the cock on the top of the top plate, (18-size full plate movement) then taking the plate in your left hand, and tool (shown in Fig. 146) in your right, place H in position, so that the end of the screw A' rests on the jewel in the balance cock, and notice the position of the arm E' which corresponds to the balance arm, between the top plate and under side of balance cock. If the distance between the arm E' and end of screw A' is too great, the arm E' will be too low and touch the plate; if not enough, it will be too high and touch the regulator pins. Therefore, all that is necessary to do is to move the screw A A' up or down as the case may be, sufficiently to ensure that the arm E' will assume the position the arm of the balance is to have. Take an 18-size balance with over-sprung hairspring, the arm is at the bottom of the rim; in that case, when measuring, the screw A' is adjusted so as to bring the arm E' close to the plate, when A' is resting on the balance jewel; if the balance is old style with undersprung hairspring, the balance arm is at top of rim, in which case A' is adjusted so that the arm E' is close to the balance cock; if the balance arm is in the center of the rim, as in some English and Swiss balances, the screw A' is adjusted so that the arm E' is midway between the plate and cock.
The reason the part A, B, D, A', is arranged to move laterally in slot C is, because all balance shoulders are not the same distance from the center, and where, in some cases, the screw A' would be in a line with the center of the staff when the arm E' was resting on the balance seat, in other cases it would reach past the center, of course, short of it; and, therefore, it is made adjustable to suit all cases.