| Name and Model Number | Keuffel & Esser 4104 Mystery 2O Inch |
| Country of Origin | USA |
| Date of Manufacture | 1945 |
| Front Scales | 50cm / A [ B CI C ] D L | K |
| Back Scales | Slide: [ S A T ] ; NBS Circular No. 47 Conversion Table |
| Scale Length | 20" (25 cm) |
| Type of Rule | Slide Rule |
| Construction | Celluloid on mahogany |
| Area of Use | Generic |
| Comment | Mystery rule with model number 4104 not appearing in any K&E catalog.
Scale set similar to N4053-5 except for location of L and K scale and the inclusion of A scale on reverse. Serial No. 118637. |
| Rarity | RRR |
| Donor | Collection of Dr. Paul J. Tarantolo Jr. |
| Match Number | 38 |
| 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. |