Client asked me to calculate flow-through for product (example being bottled beverages) to track for evidence of theft..

Problem is I can't for the life of me either think of a logical formula for it, or make sense of the data I am getting.


What I've settled on for a basic formula=

(Starting inventory + Number purchased) - (Ending Inventory + Number sold) = net change in inventory

But I'm drawing a blank on the next step, and I don't know why. Usually I'm good at this stuff


Some weeks the net change was +, some was -, but trying to think of how to tie it together to determine theft?

Also the shitty thing is, purchases are M, W, F.
Inventory is done Friday.
Sales for week go from Monday - Saturday.




Any thoughts?