Least count of a voltmeter = Value of the smallest division on its scale
Least count = Range of the voltmeter ÷ Number of divisions on the scale
Least count = Difference between two consecutive marked values ÷ Number of small divisions between them
For a digital voltmeter, least count = Smallest change in reading displayed
Check the maximum range of the voltmeter
Count the total number of divisions on the scale
Divide the range by the total number of divisions
The result is the least count of the voltmeter