| Name and Model Number | Keuffel & Esser 4135 Power Computing Rule |
| Country of Origin | USA |
| Date of Manufacture | 1913 |
| Front Scales | A [B, C ] D |
| Back Scales | I.H.P [ Index Mark FIRING STROKES PER MIN. ] [ STROKE M.E.P. ] CYL. DIA. |
| Scale Length | 5" (12.5 cm) |
| Type of Rule | Slide Rule |
| Construction | Celluloid on mahogany. Two slides and no indicator. |
| Area of Use | Generic |
| Comment | Special slide rule for use by power engineers to
make calculations specific to steam and gas engines. |
| Rarity | RR |
| Donor | Collection of Dr. Paul J. Tarantolo Jr. |
| Match Number | 40 |
| 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. |