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Reading a vernier scale
- Notice that there is a fixed scale and a sliding scale.
- The boldface numbers on the fixed scale are centimeters.
- The small marks on the fixed scale between the boldface numbers are millimeters.
- There are ten small marks on the sliding scale. The left-most mark on the sliding scale will let you read from the fixed scale the number of whole millimeters that the jaws are opened.
- In the example above, the leftmost mark on the sliding scale is between 2.1 cm and 2.2 cm, so the number of whole millimeters is 21.
- Next we use the sliding scale to find the tenths of millimeters. Notice that the ten marks on the sliding scale are the same width as nine marks on the fixed scale. This means that one of the marks on the sliding scale will align with a mark on the fixed scale; the others will miss.
- The number of the aligned mark on the sliding scale tells you the number of tenths of millimeters. In the example above, the 3rd mark on the sliding scale is in coincidence with the one above it, so the caliper reading is (21.30 ± 0.05) mm.If two adjacent marks on the sliding scale look equally aligned with their counterparts on the fixed scale, then the reading is half way between the two marks.
- On those rare occasions when the reading just happens to be a "nice" number like 2 cm, don't forget to include the zero decimal places showing the precision of the measurement and the reading error. So not 2 cm, but rather (2.000 ± 0.005) cm or (20.00 ± 0.05) mm.
 Modern digital calipers
These make the readings much easier - but do not require much skill in reading - therefore they would not be used to assess your 'high level skill' in reading instruments!
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