This really isn't an Excel question but there are sharp people out
there that might know what I'm looking for.

For a POSITIVE number (like +2, +68, +106), the value of the rightmost
digit is the rightmost digit. For example:

1 = +1
2 = +2
3 = +3
etc

But, for a NEGATIVE number (examples, -1, -17, -543), the value of the
rightmost digit is an alphabetic- or special-character. Something
like:

A = -1
B = -2
C = -3
etc.

What term describes this numbering-scheme?

Hello,

=CHAR(56.5-(SIGN(A2)+(A2=0))*8.5+RIGHT(A2,1))

I changed your request to make the task consistent: -10 will result in
"A", -1 in "B" ...

Regards,
Bernd

And the answer is:

Rightmost
Digit Character

+0 {
+1 A
+2 B
+3 C
+4 D
+5 E
+6 F
+7 G
+8 H
+9 I

-0 }
-1 J
-2 K
-3 L
-4 M
-5 N
-6 O
-7 P
-8 Q
-9 R