| Name and Model Number | Psychrometric Computer |
| Country of Origin | USA |
| Date of Manufacture | unknown |
| Front Scales | Relative Humidty – High Scales |
| Back Scales | Relative Humidty – Low Scales |
| Scale Length | 11.35" diameter |
| Type of Rule | Disc |
| Construction | Plastic on aluminum and plastic discs |
| Area of Use | Technical |
| Comment | For calculating relative humidity.
Made for the Bureau of Aeronautics by Virginia Plak Co., New York. The Smithsonian Institution has a similar calculator by a different manufacturer. |
| Rarity | RR |
| Donor | Collection of Clay Castleberry |
| Match Number | 265 |
| 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. |