Vernier calipers

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The vernier principle has long been applied to a measuring tool to which it gave its name, the vernier calipers.

It is used for accurate measuring, much as a micrometer is used.

The fact that the head of the vernier calipers can be moved along the bar makes its range of measurement much greater than that of a micrometer.

Vernier caliper

While the vernier principle is, of course, the same whether used on the micrometer or on the vernier caliper, there is a difference in application. On the micrometer, the vernier remains stationary and the scale is moved. On the vernier caliper, the scale is fixed and the vernier plate, attached to the adjustable jaw, moves with it.

This vernier plate has 25 graduations on it. The sum of the length of these 25 graduations is equal to the sum of 24 graduations on the bar. Each of the divisions on the bar is .025 inch long because the inch has been divided into forty parts. Just as the vernier on the micrometer indicated tenths of divisions, this vernier indicates twenty-fifths of a division.

A twenty-fifth of .025 is 1 one-thousandth, so we read thousandths on the vernier scale. These thousandths are added to the reading on the bar. A vernier setting which indicates 1.436" is obtained by noting the exposed figure 1. The line over the 0 on the vernier is one division past the 4, so we mark down the 4, and the reading is then 1.4.

To this we add the one division which is equal to .025 and so obtain 1.425. To this is added the number of the line on the vernier which coincides with a line on the scale. This number is 11; that is, .011. Adding this to the 1.425 we get 1.436".