Formula picking up same number twice but it should only be counted once

I am working on a spreadsheet were I am trying to determine how many trucks have come through our shipping yard on a daily basis. I need to enter each date, bill of lading and product. Some BOLs can have multiple products so the BOL will show up a couple times on the spreadsheet. We determine the number of trucks by the bill of lading. So if on 5/1/13, we had one truck stop by with three products the same BOL will be entered three times. Is there a certain formula or recommendation of how to resolve this issue? I have tried the IF, SUMIF and CountIF – but I can’t determine a way to have this truck show up as 1 instead of 3. Thanks for your help. Matt