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35.4 INSTRUMENTS

35.4.1 Vernier Scales

•Vernier scales have normal scale components, but also incorporate a small secondary scale that subdivides major increments.

•This secondary scale is based on a second scale that is one increment shorter than a main scale. If the secondary scale is compared to the main scale, it will indicate relative distance between two offsets.

	Main scale	0.4
		+0.08
		=0.48

0 1 2

.2

0

Vernier scale

•The scale pictured above would normally be on an instrument, and the main and vernier scales would slide relative to each other. The ‘0’ on the vernier scale would be used to take the reading from the main scale. In this example the main scale would read a value that is between 0.4 and 0.6. (Note: it is not considered good practice to round this to 0.5)

•The vernier scale can then be used to find the internal division, by looking for where the divisions in the top and bottom scales align. In this case the second internal division aligns with 1. Using the values on the vernier scale, we can see that the value for this division would be 0.08. The value from the vernier scale is added directly to the main scale value to get the more accurate results. 0.4+0.08 = 0.48.

•On imperial sliding vernier scales the main scale divisions are 0.050” apart, and on the vernier scale they are 0.049”, giving a reading of 0.001” per graduation.

•On metric sliding vernier scales the main scale divisions are 1mm apart, and the vernier scale they are 0.98 mm, giving a reading of 0.02mm per graduation.