What's the difference between the incremental encoder and absolute encoder? How to choose when making a servo system?

Commonly used type of incremental encoder, if you have any strict requirements on the location, zero type with absolute encoder. Servo system to specific analysis, see applications.

Speed measurement with commonly used incremental encoder, unlimited accumulation measurement; Measured in absolute encoder, location uniqueness (single or more times), finally see applications, in order to realize the purpose and requirements.