I just went through this. I had 25 eggs from a broody hen. Apparently my other hens were laying on top of her while she was setting. Was quite a mess. Anyway i had a bunch of eggs in different stages of incubation. My poor broody couldnt set on all of those so we left her with 9 and took the rest to the incubator. I looked up how to check for viability of the eggs. The article said to use a cup or bowl of baby bottle warm water and gently float the eggs. If they float they are good. If they sink to the bottom they arent viable anymore. We candled them first to check for chicks or embryo and found alot that either never developed or werent good. What we saw with the good eggs was awesome. Some of the eggs jumped, wiggled, and moved. Was exciting to see. Have 3 hatched so far and 6 more to hatch. Mamma hatched 4 for herself before giving up to care for her chicks. Dont know if this helps you or not but it sure helped me. Good luck