I understand your question. I count every chick that emerges alive. My point is that counting eggs making it to lockdown isn't representative of hatch rate since they haven't actually hatched yet, and not all of them do.
I've only got one incubator, and no hatcher, so right now, I can keep track of how many died/culled. I'm trying to track my costs per chick, so I can determine if it is actually cheaper than ordering chicks.Sew, I like the idea of waiting 24 hrs for any I have to cull, but honestly, I would forget. So I mark it by how many hatched.
