The Fell All-Way precision level, one of the first successful American made bull's eye levels for machine tool use, was invented by William B. Fell, Rockford, Illinois prior to WWII in 1939. The device was unique in that it could be placed on a machine bed and show tilt on the x-y axes simultaneously; eliminating the need to rotate the level 90 degrees. The level was so accurate it was restricted from export during World War II. The device set a new standard of .0005 inches per foot resolution (five ten thousands per foot or five arc seconds tilt). The level's production stopped around 1970. Production restarted in the 1980s by Thomas Butler Technology, Rockford, Illinois, but finally ended in the mid 1990s. However, there are still hundreds of the highly prized devices in existence.