A Vernier calliper is a device that utilized to measure the distance between two opposite sides of an object. It can be as simple as a scope with inner or outer-facing points.
The Vernier Calliper contains of a main scale fitted with a jawline at one end. Another jawline, covering the vernier scale, transfers over the main scale. When the two jawline are in contact, the zero of the main scale and the zero of the Vernier scale should correspond. If both the zeros do not accord, there will be a positive or negative zero error.