The Magnetic Rotary Encoder board is based around the Austria Microsystems AS5040 chip. This chip allows you to sense the rotational position of a magnet. Sounds boring, right? Wrong! When you combine this chip with a motor, a motor driver, and an Arduino it allows you to create a servo motor of unlimited size and rotation. You can measure the rotation of the motor and control it so that it goes to the position you desire. Or, in the case of our extruder, you can measure the speed of the motor and have it rotate at exactly the speed you desire, regardless of the load on the motor.