DIAGNOSIS That's a sign the gauge itself is out of calibration, which happens. The weighted regulator controls the actual pressure by venting excess steam; the gauge is just a visual indicator. If they disagree, trust the weight. A faulty gauge reading high is a typical failure mode.
FIX First, test for a clog. With the canner cool and depressurized, remove the gauge by unscrewing it from the lid (it just screws in). Look at the small hole on the underside—use a fine wire or pin to gently clear any mineral deposits or food particles from the gauge's inlet. Reinstall it and do a water-only test run to see if the reading is more reasonable.
IF THAT DIDN'T WORK If it's still reading high (or low), the gauge's internal mechanism is likely faulty. Gauges on these canners are not user-repairable. You need to replace the entire pressure gauge assembly with a genuine Presto part made for this model.
HEADS UP Canning at an incorrectly perceived high pressure isn't necessarily unsafe if you're using the weighted regulator correctly, as that's what actually limits the pressure. However, for accurate processing, especially with low-acid foods, you should get the gauge replaced or tested. Some county extension offices offer gauge testing services.