Lotus 123 had a function that Excel doesn't

I had to change your "-" and "+" around

Yes, the example was just that...

But when I went to a large number I got a #value# error on only one response- which really threw me (see attached).

The amount of characters that an XL cell can contain is limited, in XL2007 for ex. the limitation is 32767 characters, so to avoid errors you would put a MIN into the REPT function

D10: =REPT(IF(B10>=A10,"-","+"),MIN(32767,ABS(INT((B10-A10)/100))))

On earlier versions the limits will be different (lower) .. and/or the amount that can be viewed (outside of the formula bar) will vary... probably a good idea to avoid so many in the first instance...

Now- can this be turned into a macro or custom formula?

Confused, why do you wish to do that ?

General rule of thumb, Custom Functions (UDF) are slower than native functions...