The Zero-Power Flight Computer

The E6B flight computer, a circular slide rule developed by Philip Dalton in the 1930s, became the standard navigation aid for pilots during WWII and beyond. Its front side functions as a specialized circular slide rule with aviation-specific scales for fuel, speed, and unit conversions, while the back side is a graphical wind triangle solver. Despite GPS making it largely obsolete for practical navigation, flight schools still teach it because it builds intuitive understanding of flight math. The device requires no power, is lightweight, cheap, and nearly indestructible — making it a reliable backup. Dalton's design was adopted by the Army Air Corps as the E6B in 1938 and has remained essentially unchanged since.