Please explain this...

The principle of Vernier Callipers 

There is a theorem in advanced mathematics that guarantees the coinciding of one Vernier scale division with one of the main scale division. But discussion of that theorem is well beyond the scope of 12th standard.

However, evaluating the least count of vernier  callipers exists.

N-1 number of main scale divisions coincides exactly with N Vernier scale divisions thus 1 vernier scale division = (N-1)/N main scale division.

Now the least gap between division of main scale and vernier scale becomes 1-(N-1)/N = 1/N = LC
Now from the above theorem it holds that at last one division of vernier scale must coincide with the main scale generally vernier scale has 10 divisions thus LC becomes 1/N = 1/10 mm

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