Steel is the world's most popular construction material because of its unique combination of durability, workability, and cost. Methods for manufacturing steel have evolved significantly since industrial production began in the late 19th century. Today, steel production makes use of recycled materials. A top U.S. steel manufacturer, "Metals, Inc.," (name withheld) purchases scrap metal and melts it into steel billets either to sell or to cast into other finished goods for sale. Despite the high stakes, the quality measurements for each batch are not available until the last few minutes in the 90-minute melting process.