📖 Complete User Guide

• Click "➕ New Comparison" or use a template button to start.
• Enter Price and Amount for each option.
• After filling all fields, click the "🔍 Compare" button inside the group header – the calculator then highlights the ⭐ BEST value.
• The 🛒 Basket (at the bottom) automatically collects the best item from each comparison group – you don’t need to click anything.

• Use preset buttons (Canned, Bone‑in, etc.) or drag the slider (0‑85%).
• Higher waste = higher true cost per ounce.
• Common waste values: 35% for canned in liquid, 40% for bone‑in meat, 25% for fresh produce, 0% for rice/oil/milk.

• Each item has a "Usage" slider (0‑100%). Set the percentage you expect to actually consume.
• Example: 100% for milk you'll finish, 25% for a bulk jar of mayo that will spoil.
• The true cost increases as usage decreases.

• Toggle the switch at the top of the calculator.
• Example: 16oz vs 1kg becomes both expressed as price per 100g.

• Use the dropdown next to "Auto-Convert".
• Click "Apply" to update all cards.

• Global currency affects all cards that haven't been manually overridden.
• Each price has its own currency selector – change it for that specific product.
• The 💱 currency pill at the bottom of each comparison shows live exchange rates between different currencies used in that group.
• The 💰 Basket Total has two displays: the header card (dark gradient) shows the total in the global currency; the footer basket includes a currency dropdown to convert the total into any currency present in your comparisons.
• You can also change the per‑group currency dropdown (next to the group’s total) – this only converts that group’s best item price for display, without changing the underlying cards.

• Click the purple button "🔄 Update Currency Exchange Rates" (appears both in the top bar and in each comparison footer).
• Rates are updated automatically on page load, but you can refresh manually at any time.

• In each card, next to the 📦 Amount field, you see: × [1] 🧮 Unit(s) per package.
• Change the default 1 to the number of individual units inside the package.
• Enter the price for the whole package.
• The calculator multiplies Amount × Units per package to get the total quantity, then calculates true cost per single unit.

🧮 Example 1 – Cereal bars (grams)

• A box contains 12 cereal bars, each bar weighs 30 g.
• Enter Amount = 30 g (weight of one bar).
• Set Unit(s) per package = 12 (number of bars).
• Price for the whole box = $4.80.
• Effective total weight = 30 g × 12 = 360 g.
• True cost per gram = $4.80 ÷ 360 = $0.0133/g → about $0.40 per bar.

🧃 Example 2 – Juice boxes (milliliters)

• A multi‑pack contains 4 juice boxes, each box is 250 ml.
• Enter Amount = 250 ml (volume of one box).
• Set Unit(s) per package = 4 (number of boxes).
• Price for the whole pack = $2.00.
• Effective total volume = 250 ml × 4 = 1000 ml (1 L).
• True cost per ml = $2.00 ÷ 1000 = $0.002/ml (or $2.00/L).

• Scroll through the template buttons (Meat, Seafood, Dairy, etc.) and click any template to instantly create a new comparison group.
• You can then edit the price, amount, waste, and usage as needed.

• ➕ Option – Adds a new blank card to the current comparison group.
• ✕ Delete (on each card) – Removes that option (requires at least one card remaining).
• Delete comparison group – Click the red "Delete" button in the group header to remove the whole group (keep at least one group).

• Click the text field at the top of each card to rename the option (e.g., "Name Brand", "Store Brand").
• The group name can be edited by clicking the text field in the group header.

• After the calculator highlights the ⭐ BEST option, click the "🛒 Basket" button (in the group header).
• The item is added to the basket at the bottom of the page, and the total updates instantly.
• Click "Clear All" to start a new shopping trip.
• The basket saves automatically in your browser – your list persists even after refreshing.

• Inside any card, click the "📷 Scan Barcode" button.
• Allow camera access when prompted.
• Hold the barcode in front of the camera – the scanner will detect it automatically.
• The product name, weight, and appropriate waste preset (e.g., 35% for canned goods) are filled for you.
• You must still enter the price manually – the scanner only pulls product details from the database or Open Food Facts API.

• 📤 Export – Saves all your current groups, items, settings, and basket as a JSON file. Great for backup or sharing.
• 📥 Import – Load a previously exported file to restore all data.
• 🗑️ Reset – Clears everything and restores the default two comparison groups (Tuna and Chicken).