I agree I use 2 seperate thermometer in mine I have digital incubators as well I pay no attention to what it says it is because it's never right. Go on ebay there are a lot of one's on there or I can share my link to the 2 I have that work fantastic!!!
To momma coop. Take a thermometer and place it directly on a 3-4 testereggs it can take up to 2 days to calibrate an incubator and patience is key. If Temps are to low you will end up will underdeveloped eggs and possibly week chicks if any do hatch.. vice versa to hot will cook them. 99.9 is...
Wasn't sure if I had a pic but I found one. I use a bigger sponge now but.. This is one from tractor and supply I have 2 just like this. I have fit almost 40 at a time pull out any bad ones still have hatched at least 30 in it. If you do build one please post pics.
The biggest thing is making sure you flip the eggs. The water reservoir in the bottom works good for the first few weeks when humidity is low. For lock down I put a plastic sandwich container with a sponge that fits perfectly in it so the baby chicks don't drown. I am always about DIY but I saw...
I have had several hatches with the still air incubator I use both still and forced. The downside is the flipping but I have had an 80% hatch rate in the ones from tractor and supply I have 2 :) the key with using the ones from there are to make sure you have a thermometer and a seperate one...