UNIT THREE          USING VERNIER, DIAL, AND DIGITAL INSTRUMENTS FOR DIRECT MEASUREMENTS                                                                                      121

                                          Additional partial                                                          27 +       millimeters showing on the main scale
                                          millimeter to be read
                                          on the vernier
                                                                                                                                 millimeters showing on the vernier scale
                                                                                                                                 millimeters is the total caliper reading   Figure C-86 Reading a metric
                                                                                                                                                                            vernier caliper with .02-mm

                         27 mm +
                         showing on
                         the main scale
                                                                               The coincident point of the vernier scale
                                                                               and the main scale occurs at the 18th
                                                                               vernier division, corresponding to .36 mm

                                                                  50 division vernier scale with each division equal to .02 mm

the main scale at the eighteenth vernier division. Since each
vernier scale spacing is equal to .02 mm, the reading on the
vernier scale is equal to 18 times .02, or .36 mm. Therefore,
.36 mm must be added to the amount showing on the main
scale to obtain the final reading. The result is equal to
27 mm + .36 mm, or 27.36 mm.

These measuring tools are designed to measure the depth of
holes, recesses, steps, and slots. Basic parts of a vernier depth
gage include the base or anvil with the vernier scale and the
fine-adjustment screw (Figure C-87). Also shown is the
                                                                                                                Fine adjustment clamp                                                    Fine adjustment screw
graduated beam or bar that contains the true scale. To make
accurate measurements, the reference surface must be flat
and free from nicks and burrs. The base should be held firm-
ly against the reference surface while the beam is brought in
contact with the surface being measured. The measuring
pressure should approximately equal the pressure exerted
when making a light dot on a piece of paper with a pencil.                                                              Base clamp                                                    Vernier scale
On a vernier depth gage, dimensions are read in the same
manner as on a vernier caliper.

SELF-TEST: READING INCH VERNIER                                                                                                                                                                          Base

Determine the dimensions in the vernier caliper illustrations
in Figures C-88a and C-88b.

SELF-TEST: READING METRIC VERNIER                                                                           Figure C-87 Vernier depth gage with .001-in.
CALIPERS                                                                                                    discrimination.
Determine the metric vernier caliper dimensions illustrated
in Figures C-89a and C-89b.
                                                                                                            MECHANICAL DIAL INSTRUMENTS
                                                                                                            FOR DIRECT MEASUREMENT
                                                                                                            In recent years, many types of mechanical dial measuring
GAGES                                                                                                       instruments have come into wide use. These instruments are
Determine the depth measurements illustrated in Figures                                                     direct reading and require no interpretation of a vernier.
C-90a and C-90b.                                                                                            They are extremely reliable and easy to read. Mechanical-dial

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