Over the years, the city has been home to other large corporations in the central United States, making Denver a key trade point for the country. Several well-known companies originated in or have relocated to Denver. William Ainsworth opened the Denver Instrument Company in 1895 to make analytical balances for gold assayers. Its factory is now in Arvada. AIMCO (NYSE: AIV)—the largest owner and operator of apartment communities in the United States, with approximately 870 communities comprising nearly 136,000 units in 44 states—is headquartered in Denver, employing approximately 3,500 people. Also, Samsonite Corp., the world's largest luggage manufacturer, began in Denver in 1910 as Shwayder Trunk Manufacturing Company, but Samsonite closed its NE Denver factory in 2001, and moved its headquarters to Massachusetts after a change of ownership in 2006. The Mountain States Telephone & Telegraph Company, founded in Denver in 1911, is now a part of telecommunications giant Lumen Technologies (previously CenturyLink).