• Tags: vernier, least-count, zero-error
• Difficulty: Foundation

The vernier caliper measures lengths with precision of 0.01 cm (0.1 mm). It consists of a main scale and a sliding vernier scale. If n vernier divisions equal (n-1) main scale divisions: 1 VSD = $\frac{n-1}{n}$ MSD. Least count LC = 1 MSD - 1 VSD = $\frac{MSD}{n}$. For standard calipers: 10 VSD = 9 MSD (each MSD = 1 mm), so LC = 1 - 0.9 = 0.1 mm = 0.01 cm. Reading: MSR (main scale reading before the zero of vernier) + VSR x LC, where VSR is the vernier division coinciding with any main scale division. Zero error: if the zero of vernier is to the right of zero of main scale when jaws are closed, it is positive (subtract the correction). If to the left, negative (add the correction). Correction magnitude = coinciding vernier division x LC. Always check and correct for zero error before recording measurements. The vernier has three types of jaws: external $\frac{for length}{diameter}$, internal (for bore diameter), and a depth gauge (tail).