| Name and Model Number | Williams Compressor HP calculator |
| Country of Origin | USA |
| Date of Manufacture | |
| Front Scales | Compression ratio, horsepower, discharge pressure, suction pressure, cubic feet to be pumpted |
| Back Scales | Tables of piston displacement for various compressors |
| Scale Length | 7 ⅝ |
| Type of Rule | Disc |
| Construction | Plastic |
| Area of Use | Chemical |
| Comment | From the advertisment:
A handy device for quick solution of problems relative to GAS COMPRESSORS, Capacity, Horsepower, Suction, Intermediate and Discharge pressures, Compression Ratio, Efficiency, etc. Designed primarily for use by Compressor operators in the rapid solution of practical compressor and horsepower problems which arise in Gas Industry operation.s |
| Rarity | RRR |
| Donor | Collection of Wayne Harrison |
| Match Number | 408 |
| 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. |