At this point I am really confused because I browsed Internet tutorials for 6 hours ...so I definitely love you ! ;-)
After your first reply I copied and pasted the formula you wrote and it did not work.

I come from Openoffice ..I had the same sheet and a formula that worked in Openoffice (not the one I pasted at the beginning of the post). I do know that Excel will make my job easier but for now I am totally stuck.
The next step is that I have to adapt a OO Macro to Excel and I am really considering to reach the "commercial services" because I do not want to abuse of other people time and Job ;-)
Once again a HUGE Thank you !