It is important that  before you put any eggs in a incubator that you have plugged the incubator in.You have to make sure that the temperature stays between 99.5 and 103 degrees . Chicks begin hatching on day 21. If all the eggs do not hatch by day 25 or day 26  remove the remaking eggs and discard them. If  you have children candling chicken eggs is a really fun way to actually show them the development  of the chicken within the egg . What is candling ? Well candling is a method  of seeing  exactly what is going on inside  an egg without actually waiting until the egg hatches. Candling an egg, the egg needs to be lifted up from it's place in the incubator. You need to hold the further most ends of the egg, only this way can light travel into the egg and back out the other side. You  can do this by holding an egg between your forefingers and thumb very carefully. When you shine your light threw the egg the egg you are checking for any signs blood, veins, dark masses and small swishing objects . These can be used with any kind of flash light, or just holding an egg very close to a light bulb or any kind of source of light . What will define a bad egg?well when looking for an egg that is fertile, the first thing you need to know is how to identify an infertile egg. Also known as a bad egg, or a dud in some trades.