The least count is an important defining parameter for any kind of scale. It is defined as the minimum value that can be measured on the scale and is the distance between two small graduations. The least count is also significant because it is directly linked with the accuracy of an instrument and in some cases accuracy and least count are used interchangeably although they hold different meanings.
Determining the least count of a vernier caliper is a simple process and it can help make taking readings a quick and sure process using the length formula which we will discuss later. To find the least count of the vernier caliper we first need to find out the least count of the main scale of the caliper. To do this simply count the number of small divisions in between two marked units. Then divide the unit by the number of divisions. E.g 1cm/ 10 divisions = 0.1cm.
The function of the vernier scale is to further break down this reading into smaller values. Thus the smallest value of the vernier scale is the overall least count of the vernier caliper. To find out the least count of the caliper, we need to divide the main scale least count by the number of divisions on the vernier scale. These normally lie between 10 and 20 so if the main scale least count is 1mm then the vernier least count for 10 divisions would be 1/10 = 0.1mm. This means that the caliper can measure a minimum length of 0.1mm. To help you remember here is the formula:
Least Count of Vernier Caliper = Main Scale least count/ number of Vernier scale divisions
Once the least count is known for a caliper, then we can use the following formula to find any length easily:
Length= MSR + (VSR*L.C)
Where MSR = Main Scale Reading
VSR= Vernier Scale Reading
And L.C= Least Count of the Vernier Caliper
This method helps eliminate the doubt which is sometimes created when summing up the main scale and vernier scale readings where people may write the wrong number of decimal places or mix up units but if with the least count and length formula you can be sure about the values.