If it's not really about tuning or wiring. Then it belongs in here.
I have noticed on my mr2. The Afr on the gauge is one whole number different on my laptop. It's also doing the same thing on the 91 dsm of mine to as well is this comin which one is correct.
The problem is most likely what we call "ground offset". The ecu and WB controller/gauge is probably powered and grounded at different spots. This makes a voltage variation that manifests itself in what you experience. This is one of the reasons why going with a canbus based WB is a GREAT idea. Its digital signal is not affected by said offset.
Just put a new AEM wide band with the 4.9 sensor and similar thing. Measured the An 0-5 output while changing AFR from 11 to 16 and the voltage out put was no where near the supplied instruction voltages were, so meter is faulty. Gauge seems to read ok.
As mentioned, grounding is essential to the accuracy of the wideband signal, however equally important is using the correct calibration. Make sure the calibration in the ECU matches what the wideband gauge is sending out. If you still have a discrepancy then I'd suggest offsetting the calibration in your ECU until the reading matches the gauge. The gauge 'should' be reading accurately.