if we zoom in on the values in the C-3 to C-7 range (two octaves below middle C + two octaves above), you see that the difference in frequency there is pretty minimal (note that this chart is using a linear scale on the Y axis, not log like the previous two). above this range, I think the game boy will sound significantly out of tune with other MIDI-tuned instruments. makes me wonder if some of what we hear as the distinctive "sound" of authentic chiptunes comes from this aberration in tuning!