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54 INSTRUMENTS AND APPLIANCES

^ Occasionally, though, variations are found, as in Black's

Gingival Trimmers and in some varieties of chisel.
5. To meastire the amount of bevel of a blade
place the edge of the blade in the center of the circle,
with one side of the blade on the zero division. The
figure on the periphery of the circle on the line which
follows the other side of the blade will give the amount

of bevel in centigrades. The first two measurements
here given are the only ones in the list of which the
Boley gauge is capable.
Formula Names.—Dr. G. V. Black's set of instru-
ments is designed largely after the first three methods
of measurement given above, and the measurements

are placed on the shafts of the instruments in the
order given, the first measurement representing the
width of the blade in tenths of a millimeter, the second

representing its length in millimeters, and the third
the angle of the blade with the shaft. In cases, how-
ever, where the fourth measurement, as described
above, is necessary, it is placed second in the formula,
the entire set of measurements being known as the

Formula Name of the instrument (Fig. 58).

The Boley Millimeter Gauge

This instrument is sufficient for measuring all but
the angles in the blade and shank of an instrument.
The smaller gradations on the gauge are millimeters.

The instrument is capable of measuring as much as
10 millimeters (i centimeter) or as little as o.i milli-
meter (Mso inch). For measuring in tenths of a
millimeter a small scale known as the Vernier, located

Fig. 58.—Hatchet excavator showing formula on the handle. Figure i
on the end of the handle is the catalogue number.