Tax credit on pre-registration stock must be claimed with first return, subject to prescribed valuation and proof limits. Unregistered dealers whose registration takes effect are entitled to a tax credit for trading stock or raw materials held on that date if they held the goods for sale or production use, have borne input tax on purchases, furnish the prescribed statement to the Commissioner, and retain proof of input tax; the entire credit must be claimed with the first return. The credit equals the least of input tax evidenced, the tax fraction of cost, the tax fraction of fair market value at registration, or a prescribed amount. Cash-basis dealers exclude post-registration receipts/payments relating to pre-registration transactions from turnover.