it could be the incubator or the thermometer. try to scrounge up 3 or 4 thermometers from around the house. put them all in the same place out of any light. average the temperatures and take the one closest one to the average. or you could compare it to the one that came with the incubator and adjust the original however needed.
once you have one you trust, run a test batch of eggs. these can be from your own flock, or a trusted local source. with large fowl if they hatch before day 20 your temp is a little to hot. if they hatch after day 22 your temp is to cool. if you have a power outage it will delay your hatch also, so don't adjust if the power is out and the incubator cools off more than a couple degrees.
with bantams the days are 18 and 22 respectively.
if your first hatch fails don't get discouraged, it happens to most of us our first time around. typically it takes 3 hatches to really get the hang of it, and you will never stop learning. ive hatched a few thousand chicks this year alone and I still learn all the time. I also still run out and look in the incubators every morning and sometimes check them in the middle of the night.
when the time comes, and they start to hatch; do not help them out of the shell. it does more damage than you can imagine. the chicks don't absorb the yolk of the egg until they are ready to hatch, and after they have pipped through the shell. as the chick hatches the insides of the eggs slightly start to dry, the shell becomes real fragile and the chick will typically zip out in just a few hours. ive seen it take over 24 hours on a couple of cool hatches but over 30 they probably aren't going to make it. if they don't have the strength to get all the way out on their own, there is probably a much larger problem that you cant see. people have successfully helped them out after the hatch period, but there is usually a lot of bad feet. they are usually very weak and don't make it. I only help them hatch if its something very rare, or a highly needed bird. (rare breeder stock, or after an animal attack where a whole breed is lost)
