If you are anything like me, you've probably looked around and read lots of stuff on here. I thought I'd put up some posts that might be interesting.
https://www.backyardchickens.com/t/...-it-hatched-we-did-it-huge-thanks-to-everyone
float test for late hatch https://www.backyardchickens.com/t/...ng-egg-viability-for-late-or-overdue-hatching
egg cell chart https://www.backyardchickens.com/gallery/image/view/id/5061384/album/6067809
litehook, candling Bob white eggs (hope this helps) https://www.backyardchickens.com/t/682179/candling-bobwhite-quail-eggs-photos
Well. lockdown for me is Fourth of July eve. Getting closer and closer!! I'm wondering about that float test since some of my eggs are iffy. If you read the whole thread, it's supposed to be quite accurate but some how it seems that putting a living egg into water would not only chill it (even if water is warm) but I'd be worried about bacteria or something similar getting in. Let me know how you feel.
I wouldn't recommend doing the float test unless they are past due in the bator. Like If you get to 23 + days for chicken eggs. I did the float test on a few button quail eggs after they went past 21 days. I opened up all the shells that passed the float test before I tossed them and found 4 babies who were still alive. They had gone through a power outage that lasted almost 2 days and were too weak to pip. They were supposed to hatch at 18 days and I couldn't wait any longer.
my note about the float test... I found that eggs that develop to the end (like day 18-21) and die in the shell will still pass a float test. So look for 1 minute/60 seconds and rescue the eggs that wobble in the water. PUT THEM BACK IN THE BATOR...then cross your fingers
For the eggs that DID NOT WOBBLE, but still passed the test - I would open them up slowly from the air sac/big end of the shell and peel a little At a time to see if you have a live chick in there. This Is what I did 3 days past their hatch day... I would not recommend doing this before That. I did not find any live chicks when I opened up the 'non-wobblers' But they were all developed fully.
This is Just coming from my own trail and error ... and reading The literature and forum post on FLOAT TESTING and FLOAT TEST RESULTS