I don't have an answer for the first question, it's just one of those things that comes with experience.
However you may can tell better by seeing how well, cleanly, quickly, or maybe fully, the chicks jettison the eggshells.
Chicks who hatch like they should often leave the eggs looking like they never pipped because many of the shell haves separate cleanly and at a glance look like they are still complete. Either that or the shell haves will be nestled inside one another like Dixie cups. This effect IMHO is caused because there is enough humidity in the incubator to let the chick spin round and round inside the egg while applying its egg tooth to the inside of the shell.
I think that this comes from the peeps emerging fast and together. Still air and forced air incubators are different and I don't have much still air experience. But in a GQF cabinet incubator I shoot for real high humidity 70% is typical.
I suspect but can't prove that a lot of hatching troubles comes from eggs laid by poorly nourished hens and roosters. This means that the chicks are not as vigorous as they could be, requiring more time to hatch.
Going back to the chicks hatching together, the peeping of chicks hatching together spurs each chick on to make a greater effort to emerge at the same time as its brothers and sisters.
This is just another reason that staggered hatching is a zero sum game. I've had my fair share of total failures hatching eggs and if you keep at it you will too.. Every time you fail look back and see if you didn't do something that went against the basic nature of a chicken, like doing something that drew out or delayed the hatch and that may have prompted the old hens to say, "the heck with this crap, I'm out-of-here!"
Maybe what I'm trying to say is that Chickens are not like robins whose young are born blind, naked, helpless, tied to its parents, and unable to even feed themselves. Where as chickens are born fully clothed, vigorous, and able to forage for themselves as soon as they hatch as is proven every year by the billions and billions of broiler chickens who are raised totally motherless. Chickens therefor are tightly controlled by instinct and only thrive when their are allowed to followed their basic instinct, wreathe we think it's the right thing to do or not..
Crippled or deformed chicks is definitely a sign of too little humidity.
http://extension.psu.edu/animals/po...cience-of-incubation/humidity-and-ventilation
One of which hatched early this morning, and the other that hatched approx. five and a half hours ago, but he is now panting. I really hope he pulls through! So far he is the runt.
