| Name and Model Number | Keuffel & Esser 4079 Cox Duplex |
| Country of Origin | USA |
| Date of Manufacture | c. 1900 - 1906 |
| Front Scales | A [ B C ] D |
| Back Scales | A [BI CI] D |
| Scale Length | 50 cm |
| Type of Rule | Slide Rule |
| Construction | Open frame mahogany; celluloid laminate. Metal framed glass cursor. |
| Area of Use | Generic |
| Comment | No model number on slide rule. Model #4079 determined by matching the slide rule attributes with K&E catalog descriptions.
Non-adjustable riveted end posts. Stamped with "Keuffel & Esser Co". & "Pat. Oct. 6, 1891" (the Cox patent). This is an example of the first duplex slide rule. |
| Rarity | RRR |
| Donor | Collection of Ed Chamberlain |
| Match Number | 135 |
| Thumbnail (Click Picture for Details) |  |
| In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen |
| (1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD. |
| • RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| • RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale. |
| • RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale. |