I'm using an Eheim thermocontrol 50W thermostat in my 60l freshwater aquarium.
The official manual and dozens of forum posts state that the temperature is set by turning the outer blue wheel to the desired temperature and then correcting it with the red calibration wheel in order to compensate sensor deviation. All information I could find is numerous repetitions and reformulations of this information.
It's not possible to set the initial temperature with the blue wheel since it's doesn't have any anchor point, thus any number at any position on the wheel could mean the currently set temperature.
Approaches like trial and error (for the initial temperature) are not an option since that'd mean endless combinations together with the red calibration wheel.