Question

working priciple of vernier caliper that can be understood easily

Answer 1

The callipers have two scales the main scale and the vernier scale. together these scales give a measurement of the distance between the two inner faces of the jaws.
close the callipers so that the jaws touch lightly but firmly on the sides of the object being measured. look at the zero on the vernier scale. read the main scale, just to the left of the zero. this will tell you the length in millimetres. now we look at the vernier scale. we need to find the point where one of the markings is exactly aligned with one of the markings on the main scale. read the value on the main scale . this will tell youth fraction of millimetre that must be added to the main scale reading.