| Name and Model Number | Keuffel & Esser N 4102 Surveyors Duplex |
| Country of Origin | USA |
| Date of Manufacture | |
| Front Scales | D, sine d, osl&h, c, Tan, Tan I, Az |
| Back Scales | Vert ½ Sin2a, A, B, CI, C, D Hoe. Cos sq. a |
| Scale Length | 20 inches |
| Type of Rule | Slide Rule |
| Construction | Celluloid on redwood |
| Area of Use | Topography |
| Comment | I’ve seen very few with original case- great rule – see JOS articles by Richard Hughes |
| Rarity | RRR |
| Donor | Collection of Clay Castleberry - California USA |
| Match Number | 273 |
| 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. |