Vernier calipers are calipers that contain a second sliding scale, called a Vernier scale. The scale is named after its inventor, Pierre Vernier, a French mathematician. Vernier calipers are used when an object needs to be measured with great precision. The Vernier sliding scale measures the gaps in between the numbers on a regular scale. Vernier scales can measure down to the thousandth of an inch. Machinists often use Vernier calipers, as does the auto industry and scientific community. It may take some practice to accurately read a Vernier scale.
Open the calipers and place the object to be measured between the jaws. Gently close and lock the jaws in place.
Find the "0" on the Vernier scale. This is your pointer.
Read the large number scale. Record the number on the large scale that the pointer indicates. If the pointer is between numbers on the large scale, record the smaller of the two numbers.
Read the small number scale. Record the number on the small scale that the pointer indicates. if the pointer is between numbers, record the smaller of the two numbers. This is your tenths digit.
Read the small number divisions. Count the number of division marks the pointer indicates. If the pointer is between division marks, stop before the pointer, not after. Multiply this number by the measurement each division represents. For example, if each slash is .025 and the 0 indicates the second slash, record .050.
Read the thousandth measurement. This is indicated by the pointer landing between two division marks. Measure this space by recording which line on the Vernier lines up with a division mark on the main ruler. Start at "0" and look at each Vernier line. When you find a line that matches up with a division mark on the main ruler, count the number of Vernier lines back to the left. Multiply this by .001. For example, if you had to count four Vernier lines for a match, record .004.
Sum the numbers from steps four through six. This is your measurement to the thousandth of an inch.