My thermostat operates but seems to be badly calibrated. It will hold temperature, and you can adjust that temperature, but its not the temperature it says on the dial! It goes much higher than the stated number.
For example: to get the room to 70 F, you have to set it to about 55. To keep the nighttime temp. colder around 55, you have to turn it to around 40-45 but not as far as "off". As you turn it there are some audible clicks of either the mechanism or relay as it switches on/off (I think that's what I'm hearing).
It is a 240V line-voltage thermostat that controls an electric baseboard heater.
Under the cover there are two screws (allen key I think) which I imagine might be used to calibrate the mechanism. I asked the manufacturer and they said they don't have any manuals for this 20-30 year old model.
I could just experiment but thought it was better to ask here first rather than risk making it worse... but I'll do that if I can't find any other information.
The top photo was taken when I set it back from 70 (which it overshot) to a nighttime temp.