What is the formula for the least count of a measuring instrument?

The formula for the least count of a measuring instrument is derived from understanding the most significant division (MSD) and the value of the smallest division (VSD) on the instrument's scale. The least count represents the smallest measurable amount that can be accurately read on the instrument, which is determined by the difference between the most significant division and the smallest division.

When calculating the least count, you subtract the value of the smallest division from the most significant division. This considers how finely the instrument can measure and indicates its precision. Therefore, the correct approach involves subtracting the VSD from the MSD.

The other options suggest different mathematical operations that do not correctly describe how the least count is determined. For instance, adding or multiplying values does not provide a meaningful metric for the least count, as it lacks the basis of measuring precision in this context. Using division is also not appropriate here as it implies a ratio rather than a measurement of minimum reading capability. Thus, the subtraction of VSD from MSD is the correct formula for computing the least count of a measuring instrument.