How to read a vernier caliper

Least count (resolution) of a vernier

A vernier with n divisions spread over (n − 1) mm has divisions of (n − 1)/n mm, each 1/n mm shorter than a main-scale millimetre. That difference is the least count.

Reading steps

1. Read the whole millimetres on the main scale just left of the vernier zero line.
2. Find the single vernier line that lines up exactly with a main-scale line.
3. Multiply its number by the least count and add.
4. Write the result to the least count (0.02 mm → two decimals, even digit in the last place).

Worked examples

• 0.02 mm vernier: zero past 40, line 13 lines up → 40 + 13 × 0.02 = 40.26 mm.
• 0.05 mm vernier: zero past 12, line 7 lines up → 12 + 7 × 0.05 = 12.35 mm.
• 0.1 mm vernier: zero past 23, line 4 lines up → 23 + 4 × 0.1 = 23.4 mm.

With a 0.02 mm vernier the last digit is always even (x.x0, x.x2 … x.x8). The figures 0–9 on its plate mark every fifth line, i.e. tenths of a millimetre.

Zero error: positive and negative

Close the jaws. If the vernier zero lies right of the main-scale zero the zero error is positive; left of it, negative. Correct every reading: true value = reading − zero error (with its sign). Example: zero error +0.06 mm, reading 25.08 mm → 25.02 mm. A vernier caliper cannot be re-zeroed; a digital one can (ORIGIN), a dial one by turning the bezel.

Inch vernier (1/128 in)

Many vernier calipers also carry an inch scale in 1/16 in with a vernier of 8 divisions reading 1/128 in. Read sixteenths on the beam plus the coinciding vernier line × 1/128 in.

Avoiding parallax

Look square onto the scales; at an angle the lines seem shifted. Good vernier plates are bevelled so their lines sit almost level with the main scale. KELIBRON’s readout view turns the camera square to the plate.