New2,Casportpony,,you both may laugh at me,,(and no,I havn't been in the merlot yet) but when I pull a tray of eggs out to candle them at about 2 weeks,if the tray sits for maybe 2-3 minutes I can tell by the heat retention in the egg 99% of the time if it's gonna be dark when I candle it.I hand turn eggs daily and as time gets closer to hatch if you hold an egg for maybe 30 seconds you can feel it is cooler or not staying hot.Growing chicks inside of eggs stay very warm for a very long time compared to non fertile,or very early quitters. Next time you candle eggs try it but candle them first and seperate good from bad then hold one of each in opposite hands,you can feel one getting cooler compared to the viable one.