ML-322 Psychrometric Calculator
This is a US Army ML-322/UM Psychrometric Calculator made by the Virginia Plak Company, which was founded in 1970. It allows conversion between wet bulb temperature, dew point temperature, relative humidity, and moisture vapor pressure. The front side of the device is for calculations involving degrees F, the back side is for degrees C. It has a scale for inputting the barometric pressure in the range from 32.5 to 3.0 inHg on the front and 1100 to 100 mb on the back.
A 1945 US War Department Technical Manual for the ML-322/UM may be downloaded below (45 pages):
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