When what you buy isn't what you sell — Solved
Why it is hard
Every management system assumes the unit that comes in is the unit that goes out. If you buy by weight and sell by item, or buy concentrate and sell it diluted, that maths stops working. And it is not a tidiness problem: the product changes in between, in ratios that differ every time. Left unsolved, selling prices get calculated on a made-up cost.
How we solved it
By giving up on the impossible number. Instead of tracking the exact stock of something diluted differently every day, the system tracks cost: it records what comes in, works out the average and suggests it automatically when bottles are filled. Since it knows what arrived and what was reported, the gap surfaces without anyone hunting for it.