Reading a vernier caliper and a micrometer

What it shows

A vernier caliper has a sliding vernier scale whose N divisions span N − 1 mm, so each vernier division is 1/N mm shorter than a main-scale millimetre. The vernier zero gives the whole millimetres and the vernier line that lines up exactly with a main-scale line gives the fraction. A micrometer screw gauge advances 0.5 mm per turn and its thimble has 50 divisions, so each division is 0.01 mm. If the instrument does not read zero when closed, that zero error is a systematic error: read it with the jaws closed and subtract it from every reading.

How to use

Choose an Instrument and, for the caliper, a Vernier. Press New object, read the magnified scale and type your length in mm, then press Check. Use + and − to zoom and drag the magnified view to find the aligned line. With Zero error ticked, press Close jaws (check zero) first, then Measure object and correct your reading. Tick Reading guide for highlighted lines, or press Show answer.

Parameters you can change

• Measuring instrument Vernier caliper, Micrometer
• Caliper vernier scale 10 divisions (0.1 mm), 20 divisions (0.05 mm), 50 divisions (0.02 mm)
• Zero error None, Yes (random)
• Show reading guide

Questions to explore

1. Why is a 20-division vernier scale 19 mm long instead of 20 mm?
2. If the vernier zero lies left of the main-scale zero when the jaws are closed, how do you correct readings?
3. Would you measure a 1 mm copper wire with the caliper or the micrometer, and why?