@smartbudgetsheets One trap worth adding: the per-unit comparison only works when both packs hold the same product. Grocery stores sometimes change pack sizes (a 454 g block one week, 500 g the next, a 'family pack' with fewer sheets per roll), so the unit price quietly moves without the sticker changing. In the UK, 3-for-2 promos often just revert to the regular unit price rather than a real discount - checking the unit figure the store prints and comparing against last week's receipt catches both.