Vernier caliper
An interactive vernier caliper with sub-millimeter precision. Drag the sliding jaw to measure a randomly-placed object, and learn how the vernier scale achieves ten times the resolution of the main scale.
Reading = main scale + (vernier division × 0.1 mm)
About this lab
A vernier caliper uses two scales to measure lengths with sub-millimeter precision. The main scale is graduated in millimeters, while the vernier scale has divisions that are slightly shorter — each vernier division is 0.9 mm instead of 1 mm. This 0.1 mm difference is the key to its precision.
To read a vernier caliper: first, note the position on the main scale just before the zero line of the vernier scale — this gives you the whole millimeters. Then, find which vernier line aligns best with any main scale line — this vernier division number gives you the tenths of a millimeter. The total reading is: main scale reading + (vernier division × 0.1 mm).
The principle works because the difference between adjacent vernier and main scale spacings equals the least count of the instrument. Pierre Vernier published this elegant idea in 1631, though similar concepts appeared in Islamic astronomical instruments centuries earlier. The same principle is used in vernier protractors, barometer scales, and theodolites.