[131hn]

Using continious letters for addititives values is a good idea (F+3) can be predicted easily. Yet i agree that confusing « symbols » should be avoided. Forcing UPPERCASE formeront plus using a prefix (Z might be a good one)

ZA:03 ZB:23 ZL:55 ZI:12 ZO:08

would work greatly for me

[Kwpolska]

Z can look like 2 in sloppy handwriting.