If your AFR Scaler and Offset values are modified at all, I'd suggest reloading a clean AEM startup calibration. Whether or not you converted a calibration or someone changed these values manually, there's a problem with that calibration file itself. Those options are only found through your Full-List and no one should really ever be browsing around back there.
I guess you don't know your product

IIRC some startup calibrations already come wrongly zeroed by you and while that kinda works similar to scalar and offset values of 0.5, the problem is that logging doesn't work.
And the scalar and offset can be modified - if one wants to modify the lambda range being used (i.e. narrower range for better lambda precision). One just needs to know what those two things do before playing with them.
Why not just explain him what's wrong with the calibration he most likely got from you, instead of talking general blah blah about the two options.