Up for sale is a beautiful, highly collectible Keuffel & Esser (K&E) Model 4080-5 Log Log Duplex 20-inch slide rule. This is the rare, oversized desktop model that is highly sought after by vintage tool collectors. It comes complete with its original, authentic K&E leather case.

This complete set is in Excellent Vintage Condition and is fully operational.

Condition Highlights:

Scale Faces: The faces have a beautiful, even, light-ivory vintage patina typical of well-preserved mid-century celluloid. The black and red markings are incredibly sharp and completely legible.

Cursor Glass: The glass cursor is perfectly clear with absolutely NO cursor rot or plastic chemical degradation. It slides smoothly across the scales, though it gets just slightly tighter during the last inch on one end due to natural vintage wood expansion. There is one tiny, faint hairline mark near the center (visible under close inspection in photo). It is located on the inside surface of the glass, but it is completely superficial and does not interfere with reading the scales.

Cursor rails: While light friction tracks run evenly down both outer rails, a distinct patch of localized darkening is present on the last 2 inches of one end. I took pictures of the discolored ends.

Mechanical Action: The mahogany core is straight, and the central slide moves completely smooth along the entire track.

Metal Brackets: The original silver-toned end plates and screws are structurally sound and retain a beautiful, authentic vintage patina.

Genuine Leather Case: The original case has been carefully cleaned and conditioned. It is strong, supple, and highly presentable. The item features minor cosmetic surface marks and wear consistent with normal vintage use

Authentic Markings: The back of the case features the crisp, original factory-stamped "Code 571" marking. The inside flap also has the original engineer's handwritten name "D.S. Fulks" and matching "Code 571" inventory mark.

Serial number: This specific rule features serial number 198351, which officially dates its production to 1951 according to the Keuffel & Esser historical manufacturing archives. Being a 1951 model, it features the highly desirable, updated post-war logarithmic scale configuration that advanced engineers relied on at the dawn of the space-age era.

Investment Value:

This is an investment-grade piece for the serious vintage science and engineering collector. Finding an oversized 20-inch K&E desk model is rare on its own, but finding one with a completely clear cursor, bright faces, and its original factory-stamped leather case is exceptional. Unlike standard 10-inch models, the 4080-5, 20-inch rule was produced in limited numbers and heavily utilized in design offices, making surviving, clean examples highly scarce. Its outstanding preservation makes it a historical standout that will continue to hold and appreciate in value over time.