First try the following: Turn the black rubber conductive sheaths that cover the posts where the lever arm hits. Sometimes the posts get dirty and don't conduct the electrical current properly. Why do they get dirty?--dusty environment, trips through the washing machine and dryer, etc.
If that does not solve the problem, then see our Troubleshooting/Help Guide and refer to the DIGI-WALKER section point SW-2.
If recalibraton is necessary, then see our Troubleshooting/Help Guide and refer to the DIGI-WALKER section point SW-1.