| Name and Model Number | Keuffel & Esser Decimal Keeping Slide Rule Type II Unknown Model |
| Country of Origin | USA |
| Date of Manufacture | c. 1915 |
| Front Scales | A [ B C ] D K -- Top beveled edge: inch scale |
| Back Scales | S B L T -- Bottom square edge: centimeter scale |
| Scale Length | 25 cm |
| Type of Rule | Slide Rule |
| Construction | Closed frame mahogany body with celluloid laminate scale surfaces. Frameless cursor with tabs. |
| Area of Use | Generic |
| Comment | Instructions for keeping track of the position of the decimal point on the reverse.
Curious "B" scale on back of slide. Slide extends outside frame on the right end. No model number & does not appear in K&E catalogs. Sometimes referred to as the "K&E Mystery Rule" |
| Rarity | RR |
| Donor | Collection of Ed Chamberlain |
| Match Number | 186 |
| 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. |