The Texas Magnum
The World's Longest Slide Rule, The Texas Magnum, was demonstrated on February 28, 2001 in the Lockheed-Martin Aircraft Assembly Facility at Air Force Plant 4 in Fort Worth, Texas. The Texas Magnum is 350 feet 6.6 inches and holds the world's record for the longest linear slide rule. It weighs over 300 pounds when assembled and takes 3 people to operate. The Texas Magnum was designed as a traditional Mannheim style slide rule. The A, C, D and L scales are included on the slide rule.
The Texas Magnum is a fully functioning slide rule. After assembly, actual calculations were made on the slide rule. A resident engineer asked for a calculation on the slide rule. He validated that the Magnum computation was accurate to 5 significant digits. (The operator can interpolate to six significant digits.)
The slide rule was built in sections for ease of construction, assembly, storage, and transportation. It assembles to form a single, rigid unit.
A laser tracker measuring device was used to determine the actual total length of the scales on the slide rule. The SMX Tracker 4500 measured the exact length as 350.54948 feet. The previous record of 323 feet 9.5 inches was set in 1979 at the University of Illinois.
This prototype module was made by the designers to test the construction practices. It is on loan to the museum from Skip Solberg.
You can learn more about how slide rules work on WIkipedia.