Gold and silver are tracked by weight, so buying more or selling some works in grams. Record each and your average rate and booked gains stay correct.
Buy more
Open the gold or silver asset and click Buy. Enter the Date, the Weight (g) and the Rate / gram — a Total value adds up as you go. Click Add Buy.
Buying works in grams; the Total value is weight × rate.
Sell some
Click Sell instead. Enter the Weight (g) and Sell Rate / gram. A Sale Preview shows the cost of what you're selling and the Realized P&L before you commit.
The Sale Preview shows your Realized P&L before you confirm.
Confirm with Confirm Sell. The booked gain is saved, and you'll find it under Booked P&L and Sale History on the asset's page.
Note: Buying and selling in grams keeps this different from re-valuing the whole holding — use these when you actually transact, and Update Valuation only when the rate itself moves.