Would appreciate assistance with Calculated Fields in a Pivot table.

I would like to perform a calculation which invovles a reference to the
total of a field generated in a pivot table.

I would like to calculate the average total sales for a sales team, by
dividing each sales persons total sales, by the teams total sales.

I have tried using the average function, but this only calculates each
individuals average for each sales item.

I cannot work out how to refer to totals generated by pivot tables in a
formula.

Can anyone assist?