Calibrating My Hygrometers


I know that this topic has been done to death here, just pity me and fill me in. I have two humidors that it looks like I will need to add calibrated digital hygrometers to. How can I calibrate these? How can I make sure they are accurate in their readings?

Thanks for your input. :D


Here ducky, ducky, ducky!
Take the cap of a small jar and fill it with salt. Add just enough water to this to make a liquid paste. (Not thick and not runny) Place this mixture in a double zip lock baggie. (Preferably a gallon size) Place your Hygro's in there with them making sure there's plenty of room for everything without anything touching the sides. Leave them in there for at least 12 HOURS without messing with them. 24 is better. They should read 75% if they are accurate. If not, its easier to just write what they are off and add or subtract for your reading. Example, if after testing your Hygro reads 70 place a small piece of tape on it that reads +5 and you will know to add 5 to the reading.