@leone From the 3.5.1 source....

gb.MustSee('A'); const uint8_t mode = gb.GetUIValue(); ... ... ... (void)mode; // TODO implement mode

So the various A options are not currently implemented.

See: https://github.com/Duet3D/RepRapFirmware/blob/3.5-dev/src/Accelerometers/Accelerometers.cpp#L391