What does a vernier caliper measure, and what is its least count?

• A. Only external dimensions; least count 1 mm
• B. Inside, outside, and depth dimensions; least count typically 0.02 mm or 0.001 in
• C. Electrical resistance
• D. Only depth; least count 0.5 mm

Answer: (B)

A vernier caliper is a precision measuring tool that can measure external dimensions with the outside jaws, internal dimensions with the inside jaws, and depth with the depth rod. Its accuracy comes from the combination of a main scale and a vernier scale, which lets you interpolate between the main scale marks for readings finer than the main scale alone. The smallest increment you can reliably read—the least count—is typically 0.02 mm or 0.001 inch, though some instruments may be finer. This is what gives the caliper its usefulness: you can measure a variety of dimensions with a fairly fine resolution, not just one type of measurement or one coarse step. The other options miss the versatility or the actual capability: it doesn’t measure electrical resistance, it isn’t limited to depth, and 0.5 mm is far too large a smallest increment for a vernier caliper.