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Home > Education >Vernier Caliper Information

Tips for using vernier calipers

A vernier caliper is a common tool used in laboratories and industries to accurately determine the fraction part of the least count division. The vernier is convenient 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.
When using a meter stick to measure length, for example, it is necessary to estimate the measurement's final digit (tenths of a millimeter). From the above example, the object's length was determined to be 0.4164 m, but the final digit of that measurement is doubtful since that digit was estimated. Unlike a meter stick, the vernier caliper allows the fractional part of the smallest division to be accurately determined, not merely estimated.
The vernier consists of a main scale engraved on a fixed ruler and an auxiliary scale engraved on a moveable jaw. The moveable jaw is free to slide along the length of the fixed ruler. The main scale is calibrated in centimeters with the smallest division in millimeters. The moveable 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 mm. When the vernier is closed and properly zeroed (see Figure 4), 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.
A reading is made by closing the jaws on the object to be measured. Make a note of where the first mark on the auxiliary scale falls on the main scale. 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.
Care must be taken to insure that the vernier caliper is properly zeroed. (With misuse, it is possible that the vernier will not read zero when the jaws are closed, thus leading to systematic errors.) To correct the improperly zeroed vernier, 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 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.