R-com Cordless Egg Candler
If you own an incubator then you should really have an egg candler, unless you have the ez-scope. You can actually watch the little chick developing inside the egg. Most importantly, the egg candler enables you to remove the infertile eggs from the incubator. Failure to remove the non fertile eggs from your incubator increases the risk of bacteria growth which can spread to the fertile eggs cuasing them not to hatch.
Ideally candling at 10 days for a novice should tell if the egg is fertile or not.