How a Vernier Caliper Works

A vernier caliper measures lengths more precisely than a simple ruler by using two scales that slide against each other.

1. Main scale — marked in millimetres, gives the coarse reading
2. Vernier scale — a shorter sliding scale whose divisions are slightly smaller than the main scale divisions
3. Reading: Find where the vernier zero falls on the main scale — that gives you the whole-millimetre reading
4. Precision: Look along the vernier to find which line aligns exactly with a main-scale line — that gives the fractional part

For a 0.1 mm vernier, 10 vernier divisions span 9 mm. For 0.05 mm, 20 vernier divisions span 19 mm. For 0.02 mm, 50 vernier divisions span 49 mm.