This is a Low cost controller, Analog Dial Temperature Controller. It is also called Blind Controller. This essentially means Open Loop, just control the fuel or energy input to the system to regulate heat. This is not a Blind Controller that way, it only cannot display the temperature value, that could be another reason it is called blind.
Dial cyclic timers were used to control heat, these were purely mechanical clockwork devices. They could regulate well, when the material flow (liquid) is constant and mains power is regulated. But when the job to be heated, varies in quantity, control temperature is close to ambient or when a precise control is required; closed loop controllers are used. Even a thermostat is like closed loop, as the bimetallic sensor is temperature dependent. But not good enough.
This controller is closed loop, precision controller, only the digital display of temperature is absent. Fine one deg variations may not be easy in this.
It is for J Thermocouple you can calibrate it with boiling water and Ice. Or if you have the millivolt source you can calibrate it with that. The 1K RKE 1W is the Dial Potentiometer, You have to fix a dial and Knob. Calibrate the Dial with markings of temperature.