If there are 10 minor divisions between two major divisions, one major division representing 1∘C, one minor division will be equal to:
When the mercury level is in between the divisions
When the mercury level coincides with a major division
One major division equals 10 minor division.
∴1 minor division =110major division
∴1 minor division =110(1∘C)
So, 1 minor division =0.1∘C
This is called the least count of thermometer.