Find the value of one main scale division
Count the number of vernier scale divisions
Determine how many vernier divisions coincide with how many main scale divisions
Use the formula: Least count = value of 1 main scale division ÷ total number of vernier scale divisions
If the vernier is a direct vernier, use: Least count = value of 1 main scale division − value of 1 vernier scale division
If the microscope has a screw gauge, use: Least count = pitch ÷ number of circular scale divisions
Verify the least count using the instrument’s calibration or specification label