Vernier calipers are used for more accurate measurement than that of a slide caliper. It can measure internal and external dimensions; it can also be used as a depth gauge and height gauge. Vernier calipers are available with metric and imperial graduations. A sample of vernier caliper is shown in Figure 18.16 with name of different parts. Figure 18.16 also shows the ways of three different types of measurement such as measuring external dimension, internal dimension, and depth measurement.
A vernier caliper consists of main scale and vernier scale. Each division on the main scale is of 1 mm length. The vernier scale is 49 mm long and divided into 50 equal divisions. The length of each division on vernier scale is 49/50 mm. The difference between one division on main scale and one division on vernier scale is (1 − 49/50) = 1/50 or 0.02 mm. To read the measurement, note the main scale measurement immediately preceding the zero line on vernier scale. For example, the zero of the vernier scale immediately precedes 40 mm. To this (40 mm) must be added the decimal reading on the vernier scale. Note the line on the vernier scale which is exactly coincident with a line on the main scale. Suppose 10th line on vernier scale coincides with a line on the main scale. So the reading is 40 mm plus 10 divisions of 0.02 mm. Total length will be 40 mm + 10 × 0.02 = 40.2 mm. Thus, the measurement can be done as
Figure 18.16 Vernier Caliper
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