Occasionally the motion encoder system will work as a ratchet, with readings only increasing or only decreasing. This is not a setting in Logger Pro or LabQuest App; no software change can create the problem. The issue is between the detectors on the cart and the receiver.

Try these things to troubleshoot, in order, testing after each step:

1. Confirm that the receiver is firmly in the the track grooves and is not out of alignment.
2. Turn out the room lights to see if there is an interfering light source.
3. Run the LabQuest or computer on batteries to check for a noisy power supply.
4. Look for an obstruction on one of the sensors on the underside of the cart.
5. Look for an obstruction over the transmitting LED (not the blue power light)
6. Put fresh batteries in the transmitting cart.
7. If you are using a 2.2 m track, confirm that the range switch on the underside of the cart (by the batteries) is set to 2 m.
8. Use a different cart with the same receiver. If that resolves the problem, the cart needs repair.
9. Use a different receiver with the same cart. If that resolves the problem, the receiver needs repair.
10. If no additional cart/receiver pairs are available for testing, contact Technical Support to set up a repair for both the cart and receiver.

Other issues with the motion encoder system include
Motion Encoder zero drifts when used with LabQuest App on AC power.
Motion Encoder does not measure distances over 1.2 meters.
Motion Encoder Cart turns on but does not register motion.