Gross is the top line of the settlement: add up the sale amount of every lot this consignor sold in the sale, and that's the gross. It's the starting point — all fees and the prior balance come off of it to reach the net payable. This field is read-only; you can't type a gross by hand. It's computed from the actual sale transactions, so the only way to change it is to correct or void the underlying sale.
Voided or corrected lot sales are excluded. If a number looks wrong, check the lot transactions rather than the settlement.