A Vernier caliper is a precision measuring instrument that consists of an L-shaped frame with a linear scale on it, attached to another L-shaped frame with a secondary or vernier scale which helps to determine the precise value of a measurement.
It is generally used to measure distance. between two opposite sides of a line.
It is used to measure the internal and external diameter of any hollow cylindrical specimen.
It is used to measure the depth and height/length of the given specimen. etc.