I want to run a macro that detects when a particular cell in a Range changes
and then review that range and resolve conflicts that may exist. I think I
have two possible problems:

1. How to trigger the macro when any cell in the range changes.

2. If the answer to 1 is to define a Function to which the range is an
input, how do I get it to change a cell without actually returning a value?
For example:

Function test(tt As Range)

Range("F17").Select
ActiveCell.FormulaR1C1 = "try here"

End Function

This function is called whenever a cell in the 'tt' range is change, but
when the line: ActiveCell.FormulaR1C1 = "try here"
is executed the function fails with a #value error.

Any ideas gratefully received.