To convert alphabets to numbers, Microsoft Excel contains the "code" function that converts an alphabet to it's ASCII value.
The "char" function converts it back.
To transpose it, convert the alphabet, add/subtract the transpose formula, and convert it back to a number.
A1 (basic alphabet): A
A2 (drop 2 grades): 2
A2: = char(code(A1)-2)
ps. To credit the source, I actually found the information from Yahoo! Answers, but my preferred method isn't the preferred. After having register, fill in a few pages of information, only to find out I'm not qualified to give a "Thumbs Up" to what I felt was the better solution, I gave up and decided to post it here instead.