Gross amount is the bottom-line sale price for the lot — what the buyer owes before buyer fees and what flows into the consignor's settlement. You don't type it; the system computes it from the unit price and the pricing mode.
Gross is read-only. To change it, change the inputs (unit price, weight at sale, head count) — don't try to override the total directly.
Technical section
Data model, API, and internals — visible to developers.