Accounts > Sales Orders > Sales Commission- What populates this field?

Accounts > Sales Orders > Sales Commission- What populates this field?

I'm trying to figure out what populates the field "Sales Commission" which is listed in an account under a sales order.  I would assume that the commission listed from a product would show up here but it does not.  Any help would be great as I would like to be able to view how much commission a specific account has generated under this view.