 Potentiometers and rotary encoders look similar, but are quite different. Potentiometers are adjustable resistors that can turn about 270 degrees. They usually have three pin connectors, one for either end of the full resistance and a middle pin providing variable resistance from the internal rotary wiper. That middle pin can be connected to a microcontroller's analog input to detect the pot's rotational position. Rotary encoders can be rotated continuously in either direction. They contain little switches that tick on and off as the encoder is rotated. This in turn causes the encoder's two outer pins to go high and low in different orders, depending on which way the encoder is turned. So an encoder can tell us which way it's been turned, but a potentiometer specifies its rotational position.