The Optical Encoder also called the RPM sensor, is used in certain Genie model screw drive garage door openers. (See below for compatibility) This may resolve the issue of short travel problems or drifting limits on the garage door opener. 

• Compatible with models; 2562, 2564, 2568, PowerLift®, GPower 900
• If you do not see your model on this list and have questions please contact Genie for compatibility questions
• Genuine Genie Replacement Part