In this system, you keep track of how many whistles you produce per bed, then note down the new total in a spreadsheet. The spreadsheet should have a sheet that lists the total number of whistles per-bed.

You can also note down how many whistles you've shipped to end up with your final inventory.

WhistleCrew-PerPlateInventory.xls This spreadsheet should be considered a starting point. Automate as much or as little of it as you'd like.