A rotary encoder is an electronic device that is used to measure the angular position of a shaft or an axle. It converts the angular position of a shaft into an analog or digital code. They are widely used in industrial and consumer applications such as motors, robotics, and digital devices. It is an 20-step rotary encoder with a nice clicking’ feel with breakout board, and has a pretty handy select switch (by pushing in on the knob). The unit outputs gray code so that you can tell how much and in which direction the encoder has been turned. Note This unit does not come with a knob.