The spindle defines the cut-in and cut-out temperature of the thermostat, depending on the position. It has an area of 240, where the last 27 are used to turn OFF the thermostat if necessary. The parameters LSE and HSE will define the reference temperature, according to the position of the spindle.
In the example below, we have LSE = 0°C and HSE = 15°C. If the spindle is in the middle, the reference temperature will be 7,5°C.