· How to Read an Inch Based Vernier Scale ·

Reading an inch based vernier scale by using the four step addition method explained here is a relatively easy process.
Basic Vernier Movement

The illustration above shows a basic vernier movement as used on vernier calipers and other measuring and positioning tools. The main scale is divided into .025 inch increments, with inch and .100 inch increments marked with a suitable number. The vernier scale is divided into increments of .024 inch that represent .001 inch, with each .005 inch numbered successively as 0, 5, 10, 15, 20, and 25. The .001 inch difference (.025 - .024) between marks on the main and vernier scale means that each .001 inch change in position of the vernier scale will align an adjacent mark on the vernier scale with a mark on the main scale.

The following example is presented to illustrate the four step addition method. To read the indicated value, proceed as follows:


Step #1. Assume the illustration above is of a six inch vernier caliper. Using the zero mark on the vernier scale as the index line, find the largest whole inch mark to the left side of this index line. Write it down as shown here:

3.000

Step #2: Still using the end of the zero mark on the vernier scale as the index line, find the largest .100 inch mark to the left side of this index line. The illustration above shows that there are two .100 inch increments to the left of the index line, which equals .200 inch. Record this value as shown:

3.000
0.200

Step #3: Still using the end of the zero mark on the vernier scale as the index line, record the whole number of .025 inch increments to the left of the index line. The illustration above shows that there are two .025 inch increments to the left of the index line, which equals .050 inch. Record this value as shown:

3.000
0.200
0.050


Step #4. In order to obtain a reading to the thousandths of an inch, the vernier scale is now used. Ignore the numbers on the main beam; scan down the vernier scale until you find a line on the vernier scale that lines up with any of the lines on the main beam. The illustration shows that the mark representing 17 (.017 inch) lines up exactly with a mark on the main scale. Write it down as shown here:

3.000
0.200
0.050
0.017

Now add up the four digits to obtain the correct reading:

3.000
0.200
0.050
0.017
3.267