Eggs will continue to progress through incubation as long as the temperature is at least 95 degrees F. The eggs will not sustain major damage unless below that temp for about 6 days. Over 102 is fine as long as it is no longer than 6 minutes and anything over 104 will kill them. They claim you shouldn't help them out, but I have many times. And they hatched and grew fine. But that's only after they have already began pipping. After day 26, you can crack the egg open and look at the chick. If you can withstand doing so without feeling like a murderer. And the chick will tell you what went wrong. If the chick was fully developed, but did not hatch, you need to look at your temperature or humidity. If the chick was developed and still had his yellow yolk sack attached to his stomach, then the temperature was probably too low. If, the chick was still alive with the yolk sack, his chances of making it out in such a long period were not good and the it's the same as having the temperature too low. I have many incubators now, and read several studies done by Standford on the subject in the process of building my first incubator. I built it out of a cabinet with a hatch rate of around 95%. It went well. This was some time ago. I purchased my other incubators, because I didn't feel like building them anymore....lol...You would be surprised how well the eggs will do with temperature variations going on inside the incubator. It's not about what you read on the thermometer. It's about the egg staying a constant temperature. The egg will not fluctuate temps as much as the air inside does. Just pay minor attention to the temperature on being close to 97-102 and pay more attention to the humidity. The humidity is harder to control and more important than temperature. We, can plant tomatoes in the spring and again in the fall with the same average temps, but we all know the humidity stops you from getting any tomatoes in the fall. That's why they invented greenhouses to make humidity for you in the fall. The humidity needs to stay from 45-65. If it won't go below 70, then start punching holes in the incubator 1/2inch in size and give it 20 minutes to adjust. Then repeat as necessary. If, they humidity is too low, then add water surface, not depth. Every time you open the incubator door the humidity will drop from 65 to 30 just as fast as you can close it. I hope this helps.
