Least count of the thermometer means the smallest possible value which can be measured by the thermometer.
For finding the least count of the thermometer following Procedure is to be applied.
First Observe that the thermometers is measuring the values in Fahrenheit (°F) or Celsius (°C) or Kelvin (°K)
If the Thermometer is measuring in Fahrenheit, then use the Formula for finding the Least count,
Least count of the thermometer = 1÷(Number of Parts in one Fahrenheit block).
If the thermometer is measuring in Cecius or Kelvin scale then use the Formula,
Least count of the thermometer = 1÷(Number of Parts in one Centigrade or Kelvin block).
Least count = 1÷(number of subdivision in 1 division)