Thank you Bledu for your helpful posts.

You have shown me how to calculate the quartiles for the whole dataset.

This solves part of the problem, but there is more. In...

This is great stuff guys. It's gone 5pm here in the UK so I'll get back to you in the morning. Thanks for your suggestions.

Tom

Thanks for such a quick reply. I want to store this process and be able to reuse quickly and easily... so far as it is possible ...

Presumably the picture is of one of the american consultants.

An excellent method, thank you.

Tom