The second big change in skyscraper technology came when the World Trade Center in New York City and Sears Tower in Chicago were built. Both were extremely tall skyscrapers with over 100 floors. Both buildings used large light steel skeleton frames with lots of glass windows. The World Trade Center was completed in 1972 (417 meters) and the Sears Tower (without antenna or spire) was finished in 1973 (442 meters). For 20 years, these two buildings set the standard design. However, the Sears Tower was built in a very different manner. Instead of making of making one large building, nine different vertical buildings or tubes were built at different heights. The Sears Tower has 16 double-decker elevator. Each elevator stops at two floors at the same time (i.e. Floor 31 and 32).