The vernier caliper is a measurement tool used primarily to measure external diameters, internal diameters, and depths in an industrial setting. It consists of a main scale and an auxiliary vernier scale that slides along it to allow for fractional readings smaller than the minimum division on the main scale. This allows it to measure lengths down to 1/10, 1/20 and 1/50 of a millimeter. Vernier calipers can have two scales, such as a lower millimeter scale and an upper inch scale, and include features like jaws for external and internal measurement, a probe for depth measurement, and vernier scales to read fractions of the scale unit.