Vernier Caliper:
- Least Count = 1 MSD - 1 VSD
- Standard: 10 VSD = 9 MSD, LC = 0.1 mm = 0.01 cm
- Reading = MSR + (VSD coincidence * LC)
- Zero error: positive if vernier zero is RIGHT of main scale zero (subtract); negative if LEFT (add)
Screw Gauge (Micrometer):
- Least Count = Pitch / Number of circular divisions
- Standard: Pitch = 0.5 mm, 50 divisions, LC = 0.01 mm
- Reading = MSR + (CSR * LC)
- Zero error: positive if circular zero is BELOW reference line (subtract); negative if ABOVE (add)
- Backlash error: always rotate the screw in one direction
Comparison:
| Instrument | Typical LC | Precision |
|---|---|---|
| Metre scale | 1 mm | Low |
| Vernier caliper | 0.01 cm | Medium |
| Screw gauge | 0.01 mm | High |