Average Of Pivot Subtotal

I have a pivot table with the following row data in this order: Customer - Order# - Part#. My data field is Sum of Total, ie the sum of the total $ paid for the parts by order by customer. The pivot table provides me with a total by order, ie total $ paid for parts by order, and sum of customer, ie total $ paid for all parts for all orders. If I change the sum of customer to average of customer it provides me with average $ per part but I want average $ per order. I cannot find a way to average the subtotal by customer, ie what is the average order $.