Question: what is the formula to find out the least count?
Answer: Least count can calculated using the formula;
Least Count = Length of 1MSD –Length of 1VSD.
Generally N divisions on main scale coincide with (N-1) divisions on vernier scale.
So,
1 VSD is equivalent to (N-1)/N main scale divisions.
Using the formula for Least Count, we get.
LC=1MSD–1VSD=1MSD–(N-1)/N MSD=1/N MSD.