DC motor speed control input is DC, can not directly connect AC current (such as the 220V AC) otherwise it will burn.
The positive and negative poles of the DC power supply can not be reversed, Otherwise the governor will damage.
Motor can be divided into positive and negative, when the direction of operation and expectations are inconsistent, you can change the direction of the alignment.
The potentiometer knob can change the output duty cycle of the governor, thus changing the speed of the motor.
Please allow 1-3mm differs due to manual measurement.