Question

What is meant by least count? How can we calculate it?

Answer 1

Least count of a machine or instrument is the smallest value that can be measured using that device

We can find the least count by two main formules:

1. L.C.=Value of 1 main scale division-Value of 1 vernier scale division.

2.L.C.=Value of 1 main scale division(x)/Total no. of divisions on vernier(n).

What is least count? Least count of an instrument is the size generally mentioned in millimeter indicating smallest division on a scale.

This value is nothing but the smallest size that can be measured using that instrument. This value decides how precise the instrument is.

For example, least count of Vernier Caliper is 0.02mm and that of Micrometer is 0.01mm. So, the micrometer is more precise here.
How to calculate it? The reading formula for calculation is universal. It can be written as below,


Least Count = Minimum size that can be measured with main scale alone(MSD) / the total number of divisions on vernier/circular scale(VSD).

Thus in short-form, it can be written as, L.C.=MSD/VSD.



For Vernier Caliper minimum main scale division size is 1mm and there are 50 divisions on vernier scale that is attached to the main scale. So, L.C value of Vernier Calliper is 1/50 = 0.02mm.

For Micrometer there are 50 divisions on the circular scale and minimum division on the main scale counts 0.5mm. We can calculate by the above formula L.C = 0.5/50 = 0.01mm.