Excel 2007 : Conditional Formatting by row and column numerical labels

Hello,

An array has its rows and columns marked 1-10. It shows probabilities of an occurrence specified for a row number, dependent on which column it crosses. However, for rows and columns marked with the same number it always shows 0.5, as it means probability of the occurrence when a row marker crosses "its own" column. The question: I don't know how to format the table conditionally so that it showed all "self-crossing" cells, that is row 1 vs column 1, row 2 vs column 2, etc. I have tried with INDEX, but to no avail. Could you help please? I don't want to format the cells by value but by coordinates, as I may happen to have some non-self-crossed 0.5s in the future, and I wouldn't want them formatted, for they'd obscure the view.

Thanks a lot, that's what I needed.