Loading the incubator today- humidity question.

[Pensmaster]

YES, I double checked all that in the two days I had it running. Actually I triple checked the temp, and discovered why my maple syrup was thin this year- my digital wireless kitchen thermometer was off by 3 degrees!!!

I will read up on red plugs....

When do I need to draw the line around the air cell? I see people doing that... is that a good thing to do?

I don’t draw lines anymore. Too much risk to eggs. Ie dropping.
Typically at day 7 and at 18 I make sure they are following the guidelines. Too little air cell cut back on moisture too big air cell add.
I seldom have trouble with the size of air cells. I try to keep mine at 40% for 18 days and 60% for lockdown. Once they start hatching the humidity goes way up due to the chicks added moisture at that point I leave it alone.
I also incubate one degree higher than what’s normal. But you must know your thermometer is spot on. Like the candy thermometer being off the others are usually off as well.

You’ll also notice eggs having differing air cells. This can be due to porosity of the egg shell itself. My air cells were a little on the small size this time but they seem to be doing fine 6 of 24 out and not due till this afternoon.
Sounds like you are on the right track for the hatch.