Think this is all just slightly out of my league.

Your formula works perfectly, however I am struggling to find a way to
use conditional formatting to highlight the 4 numbers used in
calculation in light blue and the number discarded in red.

I have made the changes as per your formula and reloaded the sheet

http://www.greenwichyachtclub.co.uk/racing/Book1.xls

I guess I am looking for column t to show the column number of the 5th
value counting from the left but if there is an easier way then I will
be all ears.

Thanks again in advance for any assistance.

Kind regards
Cathy