Pivot Table Percentage Calculation
 

I have the following data:

Branch ShipmentID Invoiced by 15th Invoiced
COR 123456 0
COR 234567 234567 1

There are over 7,000 rows containing data like this. By a VLOOKUP formula,
if a shipment is not invoiced, the "Invoiced by 15th" cell will be blank, and
by formula the "Invoiced" column will return a zero. So, for example, out of
all the rows, I may come up with Branch COR having 425 invoiced shipments out
of a total of 445 shipments. I cannot figure out how to get the pivot table
to give me the percentage of invoiced shipments (in this case would be 96%).
Any ideas? Please?