Lesson 2/Learning Event 2

Vernier

Vernier calipers permit precise, accurate readings using a graduated steel

rule and a movable jaw with the vernier scale. In order to use the vernier

caliper, a thorough vernier scale and the ability to read it are essential.

The steel rule of the caliper is graduated in fortieths or 0.025 of an inch.

Every fourth division represents a tenth of an inch, and is numbered as

shown in Figure 32.

FIGURE 32.

READING THE VERNIER SCALE

The vernier scale is divided into 25 parts and numbered 0, 5, 10, 15, 20,

and 25. These 25 parts are equal to and occupy the same space as 24 parts

on the rule. The difference between the width of one of the 25 spaces on

the vernier scale and one of the 24 spaces on the rule is 1/25 of 1/40, or

1/1,000 of an inch. If the tool is set so that the 0 line on the vernier

coincides with the 0 line on the rule, the line to the right of 0 on the

vernier scale will differ from the line to the right of 0 on the rule by

1/1,000 of an inch; the second line by 2/1,000 of an inch; and so forth.

The difference will continue to increase 1/1,000 of an inch for each

division until the 25 on the vernier scale coincides with line 24 on the

rule.

To read the scales, note how many inches, tenths (or 0.100), and

fortieths (or 0.025) the mark 0 on the vernier scale is from 0 mark on the

rule; then note the number of divisions on the vernier scale from 0 to a

line which exactly coincides with a line on the rule.

For example, Figure 32, shows the 0 mark of the vernier scale coinciding

with a line on the rule (see arrow). In this case, the vernier scale is not

necessary because there is no fractional part of a space to determine. The

reading is 2.350.