I just put 7 eggs in incubator today. I have a pretty basic incubator with no hydrometer. The plastic transparent dome is a little foggy and eggs are sweating so I lifted the dome slightly to provide more ventilation. How can I make sure humidity is at right level without hydrometer? Do I need one? Is sweating a bad sign? I'm using my "Raising Chickens for Dummies" book as a guide, as the incubator instruction are basic and don't mention much of anything. Help! Don't want to kill them before they even get started!