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26 THE TECHNICAL PKOCEDUBES IN FILLING TEETH.
plus of the true measurement, completing the reading. Though
the Boley gauge is not so convenient for the purpose as the
more expensive instrument gauge, Figure 17, all of the instru-
ment measurements may be made with it, except the measure-
ments of the angles of blades. Besides the measurement of
instrument blades, plugger points, burs, drills, etc., there are
hundreds of uses for it in dentistry, and its use contributes to
accuracy of observation.
There is no other one item in manual training that does
more for the acquirement of appreciation of form than that of
making many accurate measurements. In the human mouth
it is rather rare that the central incisors differ so much in width
as to be noticed by the ordinary observer, yet, with the Boley
gauge, modified by grinding the ends of the straight points mod-
erately thin so that they will go deeply into the embrasures
between the teeth, it will be found that these two important
teeth are generally not exactly the same in width. The instru-
ment should be used much for measurements in building out
broken angles of teeth and in the selection and adaptation of
artificial substitutes for lost teeth. If it was more generally
used, fewer ugly errors would be made. The man who makes
much use of delicate measurements acquires a much finer
appreciation of size and form by the eye alone than the man
who does not make such measurements.

Classification of Instruments.
One of the sioecial objects sought in this classification is
to limit the sizes, lengths and angles of blades of excavators to
a well graded, sufficient number, and exclude all others for the
prevention of that confusion which indefiniteness brings. This
can be seen and appreciated in the illustrations of the Ordinaries,
Figures 19, 20. The angles of the blades of these are 6, 12, 18
and 23 centigrades. These angles are found to be ample for
all purposes in dentistry, and no other angles of ])lade are
admitted. Angles between those given might certainly be good
instruments, or lengths and widths of blades between these also
might be good, but why have a greater variety of angles or sizes
of blades! What use does such a multiplication of indefinite
forms subserve? They create confusion without benefit, and
burden manufacturers with unending lists of indefinite forms
from which d<'ntists choose iiKlisci-iiiiiiiately, without guide, in
the formation of instrument sets, to find finally dissatisfaction
with their choice and disorder in their instrument cases. Any