Incremental rotary encoders are multi-turn sensors that use optical, mechanical, or magnetic index-counting for angular measurement. They do not contain an absolute reference. Instead, incremental rotary encoders count relative to the turn-on position. The number of successive cycles (signals) corresponds to the resolvable mechanical increments of motion.
In-depth information about an incremental encoder's operation, types, and specifications can be found on the Rotary Encoder Guide.
Absolute rotary encoders use optical, mechanical, or magnetic indexing for angular measurement. 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.