The A-B function is buggy. The original coder confused + and - signs, thus causing the display for A-B to be in the wrong place - often off the screen, so far that it does not even show up. An open issue was submitted on github. The patch is included here.
diff for the Process.c file:
diff Process.c Process_corrected.c
37c37
< s16 Posi_412, Posi_41, Posi_42, Posi_4_2, Posi_4F1, Posi_4F2, Posi_4F3, Posi_4F4;
---
> s16 Posi_412, Posi_41_2, Posi_41, Posi_42, Posi_4_2, Posi_4F1, Posi_4F2, Posi_4F3, Posi_4F4;
326a327
> Posi_41_2 = _4_posi - _1_posi + _2_posi;
539c540
< Tmp = Posi_412 + Va - Vb;
---
> Tmp = Posi_41_2 + Va - Vb;