I'm using Tableau and I have a field called Sales_Order_Date. I need to get the AVERAGE number of days between each sales order.

Example: I have 3 orders

- 01/01/2014
- 20/01/2014
- 30/01/2014

The number of days between order 1 and order 2 = 19 days The number of days between order 2 and order 3 = 10 days

The average is 29/2 = 14.5 days

How can I do this using a calculated field in Tableau for 000's of dates?