I'm trying to come up with a realtime customer account ranking formula that can be displayed on the customer record, and in reports.  This will be very helpful from a Support as well as Executive standpoint for us.

For example, customers may purchase anywhere between 2-20,000 widgets each month from our company.  We currently capture this data in salesforce in a field called 'widgets last 30'.

I'd like to compare the 'widgets last 30' value across all customer accounts in our system, and then return a value (rank) in the customer record based on this relative ranking.  We have different customer 'Types' as well (Retail, Wholesale, etc.) so it will be important to return a ranking based upon this customer Type.

I think I can accomplish this by simply creating a new field of type formula, but I'm a little lost on how to craft the formula to capture this 'ranking'.