I have a spreadsheet that users fill in for an audit. They need to enter an x
in one or four rating columns. I can limit the value entered and force an x
through validaion with no problem.

What I need to do is to allow an x in only one column. There are four rating
columns B, C, D and E. If they put an x in column B, then I do not want them
to be able to put an x in columns C, D or E. Likewise, if they put an x in
column C, then B, D and E must be blank.

How do I allow only one column to have an entry?