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.
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