ML-429 Psychrometric Calculator
Front View
Rear View
This 1961(?) US Army Signal Corps ML-429/UM Psychrometric Calculator is made of plastic and was made by the Sillcocks-Miller Company. It is 11.25 inches in diameter. When the air temperature and a humidity value are known, it allows calculation of the other humidity values, among which are wet bulb temperature, dew point temperature, and relative humidity. It has scales for calculations at 30, 29, 28, 27, 25, and 23 inHg barometric pressure. The front side of the device is for calculations at high air temperatures while the back side is for low air temperatures. It's very similar to the US Navy CP-165A/UM Psychrometric Computer, also on this website.
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