Correct option is D
In a forward Vernier scale, the length of a certain number of Vernier divisions is made equal to a slightly smaller length of main scale divisions. As a result, one Vernier scale division (VSD) is slightly smaller than one main scale division (MSD). This small difference between VSD and MSD is what allows the instrument to measure very fine distances accurately.
The principle of the Vernier scale is based on comparing these two scales. The difference between 1 MSD and 1 VSD is called the least count, which determines the precision of the measuring instrument. For example, if 10 VSD = 9 MSD, then 1 VSD = 0.9 MSD, which is smaller than 1 MSD.
