| Name and Model Number | Keuffel & Esser N4135 Power Computing |
| Country of Origin | USA |
| Date of Manufacture | 1923 |
| Front Scales | A [ B, CI, C ] D |
| Back Scales | P [ R ,W ] D |
| Scale Length | 5" (12.5 cm) |
| Type of Rule | Slide Rule |
| Construction | Celluloid on mahogany |
| Area of Use | Other |
| Comment | Special slide rule for use by power engineers to make
calculations specific to steam and gas engines. Serial No. 53681. |
| Rarity | RR |
| Donor | Collection of Dr. Paul J. Tarantolo Jr. |
| Match Number | 44 |
| 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. |