Virginia Plak / Psychrometric Circular Calculator ML-322/UM
Virginia Plak Company
USA
Plastic
1944
Ø 25 cm
Engineering
Notes: "US Army Signal Corps aid for calculating relative humidity, dew point and vapour pressure given sling psychrometer (wet and dry bulb temperatures) and barometer readings. One side is for temperatures in Fahrenheit and barometric pressure in inches of mercury. The other side is for temperatures in Celsius and barometric pressure in millibars."
