Werner,
That's exactly what I thought my first approach would do lol, clearly not!
You're approach looks far better. I was working on one, I think it might be similar to that approach?
I called it array2 as I had used array earlier as a trial, but the rows are the same so N still applies. Not sure how this differs from yours but value slightly different. I will have a look at this tomorrow and report back, but the value for Cd which yours gives is near enough perfect.
Thanks for everything