Absolute rotary encoders provide a unique output for every resolvable movement or shaft rotation. They do not lose their position after power-down, but instead provide absolute position upon power-up without requiring a home cycle or any shaft rotation. Absolute encoders use four main technologies: optical, mechanical, fiber optic, and magnetic.
Addition absolute rotary encoder information, including details about device operation, types, and specifications, can be found on the Rotary Encoders Guide.
Incremental rotary encoders are multi-turn sensors that use optical, mechanical, or magnetic index-counting for angular measurement. They contain no absolute reference, but instead count relative to the turn-on position.