Wisconsin Knife Works, having some unused manufacturing capacity, decided to try to manufacture spade bits for sale to its parent, Black & Decker, a large producer of tools, including drills. A spade bit is made out of a chunk of metal called aspade bit blank,and Wisconsin Knife Works had to find a source of supply for these blanks. National Metal Crafters was eager to supply the spade bit blanks. After some negotiating, Wisconsin Knife Works sent National Metal Crafters a series of purchase orders. On the back of each purchase order was printed “Acceptance of this Order, either by acknowledgement or performance, constitutes an unqualified agreement to the following.” A list of “Conditions of Purchase” followed, of which the first was “No modification of this contract shall be binding upon Buyer [Wisconsin Knife Works] unless made in writing and signed by Buyer’s authorized representative. Buyer shall have the right to make changes in the Order by a notice, in writing, to Seller.” The seller met the terms of the first two purchase orders from Wisconsin Knife Works. After the first two orders, National Metal Crafters was late with the deliveries. No delivery date had been specified on the purchase orders, but the delivery dates had been communicated orally between the two parties to the contract. Wisconsin Knife Works claimed that National Metal Crafters breached the contract. National Metal Crafters claimed that it had modified the dates for delivery and that Wisconsin had accepted these dates. What could constitute a binding modification after this contract was formed? [Wisconsin Knife Works v. National Metal Crafters,781 F.2d 1280 (1986).]