Thanks again for your help, but I don't think I was very clear when I asked my question. It's something like this:
"If the 'MR Suffix' in the 'PO Log Form' is the same as the 'MR Suffix' in the 'Material Category Codes and Lookup' table, then the 'Mat'l Cat Code' in 'PO Log Form' is the 'Material Category Code' that corresponds with the 'MR Suffix' record in 'Material Category and Lookup' table.
I hope I didn't confuse you as much as I have confused myself.