Does anybody know of some code which would "increase" the letter within a cell?
i.e. if the value of the cell was "A", when you select the cell and run the
macro, it would change the cell value to "B". If you did it again it would
change it to "C", etc... etc...

I have found a way to do it using a helper cell, but I'd much prefer the
macro to operate on just the one cell. My old method was as follows:
A1 starts with the value 65. The formula in B1 = CHAR(A1). (So B1 starts as
"A")
I then selected A1 and used the following macro (assigned to a shortcut to
make it quicker):
Sub Add_1()
   Selection.Value = Selection.Value + 1
End Sub

The reason for requesting this: Sometimes a cell needs to have a particular
letter value to achieve the required output in a resultant cell, but I
wouldn't know straight away what the letter needs to be. Rather than entering
"A", checking the resultant cell, then entering "B", checking again, etc...
(very slow and tedious), I could just keep my finger on the shortcut key
until I see the resultant cell flicker, signalling that I had just passed the
required letter value (much quicker).

Can anybody think of a way (maybe using CODE or CHAR or something?) for this
process to operate without the need for the number format helper cell in A1?

It's really puzzling me, and would make life a lot easier.

Thanks in advance, Neil