I did the hygrometer check on my two of my hygrometers by using salt and water and a plastic bag. http://exoticpets.about.com/od/herpresources/ss/hygrometer_6.htm Given enough time: My digital radio shack thermometer hygrometer reads 63. My reptile cage analog hygrometer reads 50. Comparing this to 75%, both are reading low. Which is good because they never seemed to get high enough. The reptile one is the one that will fit inside the incubator if it has enough stick left. Adjusting for the error I will probably strive for 30-35% for the first 18 days and 50% for the last three.