Hello! I only have done this one hatch, so not really experienced!
Our temperature didn't fluctuate. The thermometer on the incubator stayed at 37.8C, and the calibrated thermometer at the bottom usually said 37.4, but it's thermometer sensor is on the underside, so against the floor of the thermometer. So the average temperature was about right. It is a fan assisted, round incubator, much like a
Brinsea (only a slightly cheaper alternative) and I don't think we had any hot or cold spots. The egg rotator turned the egg in a 360 circle anyway (it was removed for lockdown).
We also dry hatched - the humidity was naturally between 20-30%, which was where we wanted it. For hatch, I did increase it to between 30-40%. My daughters took readings everyday, usually six times a day throughout the whole incubation, which they then averaged (as part of their home ed studies), so I do have full data set if anyone is interested!
We were hatching three different breeds, one of which was Maran which apparently prefer a dry hatch for the lockdown too. So we didn't want to raise the humidity much for the lockdown period, but when the second of the Cream Legbar's got a dry membrane after pipping, and then struggled to zip, I did add the water bottles to increase humidity to 50-60%. It did actually get shrink wrapped, and I did have to assist. The inner membrane was completely sucked onto the poor thing and it could not turn; it would not have been able to zip. It is a proper spunky lil boy now, but I'm pretty sure he knows I helped him as he ran into my hand this morning in the brooder, and settled down in my palm - so sweet.
Overall it has been an interesting journey. I may write a blog post to help me remember what we did, in case we ever want to incubate eggs again in the future, and in case anyone else can learn anything through what we did!