Full Details

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
(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.