Okay, attempting that equation gives wildly inaccurate results.
For example (analogReference set to INTERVAL2V56):
-1.47, -1.78, -1.88, -1.98...
Or (analogReference set to DEFAULT):
2.02, 1.95, 1.93, 1.91...
@Wawa your equation in #61 produces equally inaccurate results. Except it is:
2.02, 1.95, 1.93, 1.91... and -21.49, -21.80, -21.88, -21.99... depending on which way rawValue is subtracted as you noted (inverting as you suggested produces the positive values). This was tried with analogReference set to INTERNAL2V56 and DEFAULT which had the same effect as noted above.