[Greenbuilding] more than most want to know about hygrometers

[nick pine]

John Straub's buddy Terry Brannen http://www.camroden.com/TerryResume.html 
says the easiest way to measure humidity accurately is to measure the dry 
bulb air temp Tdb, then stir a glass with some ice and water until you just 
see dew on the outside, then measure the dew point temp Tdp on the glass and 
look up the RH on a psychometric chart or calculate RH = 
100e^(9621(Tdp-Tdb)/((Tdp+460)(Tdb+460))) = 
100e^(9621(50.5-70)/((50.5+460)(70+460))) = 50% with Tdb = 70 F and Tdp = 
50.5 F.

Nick