The ALPS EC09E1524417 is a 9mm, 15-resistance, 30-detent mechanical rotary encoder. This compact encoder is designed to improve performance by providing mechanical feedback and precise motion control. It is made up of an inner and outer wheel that rotates together as a unit. The inner wheel has a series of pins or contacts that, as they move around in a circle, create a low-level AC signal. The outer wheel has a series of detents, or click stops, which double the resolution of the encoder. This makes it suitable for use with LCD or OLED displays and other applications in which precision control is needed.