Principle, parts and least count (0.02 mm) of the vernier caliper, with a reading example.
The vernier caliper is a precision instrument for measuring outside, inside and depth sizes to an accuracy of 0.02 mm.
Principle
It works on the difference between two scales – the main scale and the vernier scale. In a common metric vernier, 49 mm of the main scale is divided into 50 equal divisions on the vernier.
1 VSD = 49/50 = 0.98 mm
Least count = 1 MSD − 1 VSD = 1 − 0.98 = 0.02 mm
Parts
Beam with main scale, fixed jaw, sliding jaw with vernier scale, outside measuring jaws, inside measuring jaws (nibs), depth bar, locking screw, fine adjustment screw.
Taking a reading
Example: Zero of the vernier is just past 32 mm on the main scale, and the 18th vernier line coincides with a main scale line.
Reading = 32 + (18 × 0.02) = 32 + 0.36 = 32.36 mm.
Precautions
- Check the zero error before use – close the jaws and see that both zeros coincide.
- Clean the jaws and the job.
- Do not press hard; lock the jaw and read straight in front of the eye.
- Never measure a moving or hot job.
Quick Revision
- 49 mm = 50 VSD → LC 0.02 mm.
- Reading = MSR + (VC × LC).
- Measures outside, inside and depth.
- Always check zero error first.
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