Donald A. Hall Sr. Master 20-Inch Duplex Engineering Slide Rule (1927)

Donald A. Hall's master 20-inch duplex drafting slide rule with celluloid scales on mahogany used to design the Spirit of St. Louis. — Donald A. Hall Sr. Master 20-Inch Duplex Engineering Slide Rule (1927) · Donald A. Hall Estate Collection

The supreme mathematical artifact of the 1927 transatlantic crossing: Donald A. Hall Sr.'s personal 20-inch duplex engine-divided slide rule with glass cursor runner. Engineered with precision white celluloid scale faces laminated onto seasoned Honduras mahogany to prevent thermal and hygroscopic distortion, this analog calculating instrument served as Hall's primary computational tool at Ryan Airlines. Using this rule, Hall calculated the gross weight curves, wing loading, fuel consumption rates, Clark Y lift-to-drag ratios, and center of gravity travel that enabled the Spirit of St. Louis to complete its nonstop flight to Paris. Hall hand-etched his name into the hardwood frame, preserving full provenance for this primary aerospace artifact.