| Name and Model Number | Keystone American Bule Paper #1540A |
| Country of Origin | Germany ----“ DRP No (DP) 126499”, in trough |
| Date of Manufacture | Cursor c. 1915, Probably early 1920 to 1930 |
| Front Scales | A, B, CI, C D, K |
| Back Scales | S, L, T back of slider |
| Scale Length | 12.5 cm |
| Type of Rule | Slide Rule |
| Construction | Celluloid on Mahogany |
| Area of Use | Generic |
| Comment | Mahogany with groove in trough – European style. K&E frameless with white flap type endpieces – unlabeled black cardboard case. A very diverse slide rule made in Germany with a K&E classic cursor. |
| Rarity | RR |
| Donor | Collection of Clay Castleberry - California USA |
| Match Number | 283 |
| 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. |