I recently hatched 9 perfectly formed RIR chicks in my homemade incubator. They all hatched within 22 days of being set. There is a separate thread if you care to read about the experience and see the pictures.
Here is a picture of one of the two chicks that apparently were fully developed but didn't hatch. In both cases the chicks didn't pip the internal membrane or the shell. I wish I knew what went wrong and how to avoid it in the future.
There were no temperature spikes; temps were consistently 99.7 to 100.0. The humidity was stable at about 53% until lockdown, at which time I brought it up to about 75%. There was one brief period (maybe six hours) on day 21 when the humidity rose to about 90%.
In addition to these two full term chicks, I had two other failures. I opened them and they were early quitters with tiny embryos, so I assume that was genetics or something not my fault (except that I should have culled them during early candleing.)
Edited by tracecom - 3/27/11 at 9:07am