Wikipedia:Today's featured picture (animation)/March 10, 2007
An animation showing how to use a vernier caliper, which is a caliper that uses a vernier scale to interpolate linear measurements. Vernier calipers can measure internal and external dimensions using, respectively, the uppermost and lower jaws, and also depths, using the depth probe (located at the right end). In this example, the first two digits (2.4) are decided by the location of the zero of the vernier scale in the centimeter scale, and the last digit (0.07), by the first line of the vernier scale that exactly matches a line of the centimeter scale above.
Image credit: Joaquim Alves Gaspar