The gold balance: why a gold shop needs two ledgers
In most gold shops, a regular customer’s account is not a single number. A customer can owe ten million toman for a sale and at the same time be owed three grams of melted gold. Add both into one column in toman and the real balance disappears every time the price moves.
The fix is to give every customer two ledgers: a rial ledger for money and a gold ledger for grams. Each trade leaves its own mark on both. Selling gold to a customer reduces shop stock and creates a rial debt; taking melted gold in does the reverse.