| Name and Model Number | Cox's Compressed Air Discharge Computer and Pump Computer, 1897 |
| Country of Origin | USA |
| Date of Manufacture | 1897 |
| Front Scales | Discharge Computer Scales: Compressed air discharge, Pipe diameter, Initial Pressure, Length of pipe, Loss of pressure |
| Back Scales | Pump Computer Scales: Free air discharge pressure, Air & water cylinder diameters, Lift and piston speed, Gauge pressure, Air cylinder diameter |
| Scale Length | Varies |
| Type of Rule | Disc |
| Construction | Printed cardboard |
| Area of Use | Technical |
| Comment | Used for calculations related to sizing pipes for compressed air.
Computer bears the imprint "Designed by William Cox", who patented his design for the first duplex slide rule in 1891. Published and copyrighted in 1897 by Rand Drill Company, New York. |
| Rarity | RRR |
| Donor | Collection of Mike Frey |
| Match Number | 230 |
| 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. |