CUPOL: How to use the vernier caliper

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Using a vernier caliper

Figure 1.

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A vernier caliper (or vernier) is a common tool used in laboratories and industries to accurately determine the fraction part of the least count division. The vernier is a convenient tool to use when measuring the length of an object, the outer diameter (OD) of a round or cylindrical object, the inner diameter (ID) of a pipe, and the depth of a hole. To see short videos showing how to use the vernier to measure these various dimensions, click on the links below.

Adjusting the vernier's auxiliary scale. [0:34, 8.5 Mb]
Measuring the length of an object. [0:17, 4.6 Mb]
Measuring the outer diameter of a round object. [0:40, 9.7 Mb]
Measuring the inner diameter of a hollow cylinder. [0:25, 6.4 Mb]
Measuring the depth of a hole. [0:44, 10.7 Mb]

How the vernier works

Figure 2.

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The vernier consists of a main scale engraved on a fixed ruler and an auxiliary vernier scale engraved on a movable jaw (see Figures 1 and 2). The movable auxiliary scale is free to slide along the length of the fixed ruler. This vernier's main scale is calibrated in centimeters with the smallest division in millimeters. The auxiliary scale has 10 divisions that cover the same distance as 9 divisions on the main scale. Therefore, the length of the auxiliary scale is 9.0 mm.

Zeroing the vernier

Figure 3.

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When the vernier is closed and properly zeroed (compare Figure 5), the first mark (zero) on the main scale is aligned with the first mark on the auxiliary scale. The last mark on the auxiliary scale will then coincide with the 9 mm-mark on the main scale. This is read 0.00 cm.

Figure 4.

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Once the vernier is positioned to make a reading, make a note of where the first mark on the auxiliary scale falls on the main scale. In Figure 4, we see that the object's length is between 1.2 cm and 1.3 cm because the first auxiliary mark is between these two values on the main scale. The last digit (tenths of a millimeter) is found by noting which line on the auxiliary scale coincides with a mark on the main scale. In our example, the last digit is 3 because the third auxiliary mark lines up with a mark on the main scale. Therefore, the length of the object is 1.23 cm.

Reading the vernier. [0:51, 22.3 Mb]
Self Study: Determine the length of an aluminum block. [1:00, 13.8 Mb]
Self Study: Determine the radius of a sphere. [0:50, 10.8 Mb]

An improperly zeroed vernier caliper

Figure 5.

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Care must be taken to insure that the vernier caliper is properly zeroed (see Figure 3). (With misuse, it is possible that the vernier will not read zero when the jaws are closed, thus leading to systematic errors.) The vernier in Figure 5 is improperly zeroed. To correct this, a zero correction must be made. A correction may be either positive or negative. If the first mark on the auxiliary scale lies to the right of the main scale, then the reading is too large and the error is positive. The zero reading in Figure 5 is +0.05 cm and should be subtracted from any measurement reading. Similarly, if the first mark on the auxiliary scale lies to the left of the main scale zero-mark, then the error is negative and the correction should be added from the measurement reading.

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If you have a question or comment, send an e-mail to Lab Coordinator: Jerry Hester

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