Safeguard duty calculation offsets applicable anti dumping duty for Advance Authorization imports; negative amounts treated as nil. Safeguard duty on carbon black imported under Advance Authorization is calculated by reducing the applicable safeguard ad valorem rate by the anti dumping duty amount that would be payable but for the Advance Authorization exemption; if the computed safeguard duty is negative it is treated as nil. Although Advance Authorization conditionally exempts ADD at import, the notional ADD is the reference for adjustment, and ADD becomes payable if the export obligation conditions are not fulfilled.