Quote: Ok, great thanks so much. I thought is was 70 but I should have looked it up. lol and I did not know it was not accurate.
Is there a way to set one to be accurate?
Sodium chloride is the salt that will produce the 75% humidity point. Using magnesium chloride instead will produce the 33% humidity point. The 33% humidity standard can be purchased from various sources and is in my opinion a more useful standard than the 75% humidity standard.
http://www.ambientweather.com/amwecaki.html
Unfortunately cheap hygrometers will only allow setting the humidity at a single point if at all. The most accurate results will be from setting the calibration at both 33% and 75% humidity.
The wet bulb thermometers offer the most accurate relative humidity readings as long as the "sock" is kept clean. Clogging the "sock" with dried solids pulled from the water will cause false readings with a wet bulb thermometer. Using distilled water should prevent the "sock" from plugging up.