distance between the
inner faces of the two end stones, and corresponds to the distance
between the lines _v d_, Fig. 171. This measurement can be got by
removing both end stones and taking the distance with a Boley gage or a
douzieme caliper.

A CONVENIENT TOOL FOR LENGTH MEASUREMENT.

[Illustration: Fig. 180]

A pair of common pinion calipers slightly modified makes as good a pair
of calipers for length measurement as one can desire. This instrument is
made by inserting a small screw in one of the blades--the head on the
inner side, as shown at _f_, Fig. 180. The idea of the tool is, the
screw head _f_ rests in the sink of the cap jewel or end stone, while
the other blade rests on the cock over the balance. After the adjusting
screw to the caliper is set, the spring of the blades allows of their
removal. The top pivot _z_ of the cylinder is next cut to the proper
length, as indicated by the space between the screwhead _f_ and the
other blade of the pinion caliper. The upper pinion _z_ is held in the
jaws of the cutting pliers, as shown in Fig. 177, the same as the lower
one was held, until the proper length between the lines _d v_, Fig. 171,
is secured, after which the cylinder is put back into the cement chuck,
as shown at Fig. 178, except this time the top portion of the cylinder
is allowed to protrude so that we can turn the top pivot and the balance
collet _D_, Fig. 171.

The sizes we have now to look to is to fit the pivot _z_ to the top
hole jewel in the cock, also the hairspring seat _D_ and balance seat
_D'_. These are turned to diameters, and are the most readily secured by
the use of the micrometer calipers to be had of any large watchmakers'
tool and supply house. In addition to the diameters named, we must get
the proper height for the balance, which is represented by the dotted
line _b_. The measurement for this can usually be obtained from the old
cylinder by simply comparing it with the new one as it rests in the
cement chuck. The true tool for such measurements is a height gage. We
have made no mention of finishing and polishing the pivots, as these
points are generally well understood by the trade.

REMOVING THE LATHE CEMENT.

One point perhaps we might well say a few words on, and this is in
regard to removing the lathe cement. Such cement is usually removed by
boiling in a copper dish with alcohol. But there are several objections
to the practice. In the first place, it wastes a good dea