How to display an average of a dimension?

[#1]

Hi all,

I was wondering if there is a way of getting an average in a text box of a calculated dimension in a table?

What I'm needing to do is show the average amount of days before an order is discharged. So in the table we have start of order and end of order then for the expression in that table is the days between the 2. From this we need to see the average of all the days in a text box.

Can anybody help?

(Can answers be put really simply as I'm not the most technical person! )

Hope this kind of makes sense....

Many thanks in Advance