When you select FIX, SCI or ENG mode in the HP67 it stores 22, 00 or 40 in nibbles 5 & 4 of ram[62]. It works like this:

[f] [FIX] ...
07015: jsb 07261
07016: load constant 2
07017: load constant 2
07020: if n/c go to 07027

[h] [ENG] ...
07021: jsb 07261
07022: load constant 4
07023: if n/c go to 07026

[g] [SCI] ...
07024: jsb 07261
07025: load constant 0
07026: load constant 0
07027: c -> data register 14
; if FIX then C=nnnnnnnn22nnnn
; if ENG then C=nnnnnnnn40nnnn
; if SCI then C=nnnnnnnn00nnnn
...

07261: ... ; (select ram bank 3)
07264: data register -> c 14 ; ram[48+14=62] -> c
07265: p <- 5
07266: return

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