My P4P is giving me good AGL altitude data in the downlink, and the Lat/Long GPS results are spot on. But the GPS altitude recorded in the EXIF photo data is showing ~ 20 meters below sea level when I'm really ~ 140 meters above MSL. I can't figure out what calibration might do that, but I'd have thought that a bad GPS unit would be bad all the way around. What am I missing? Can the GPS Z-axis really be that far off as a normal function?