I've been running the incubator dry for a couple of days.
It started at 40% humidity and slowly dropped to 30%.
It got down to low 20's after a day. I opened the lid and let in some moist air.
On about day 16 I'm going to add water by misting the eggs directly.
That's what I did in desperation when hens were hatching in my bone dry room in January.
I wish I had a hygrometer then. I'll bet it was < 10%.
Both hens hatched eggs and it wasn't just low humidity, it was almost NO humidity.
Those birds were Dorothy & her siblings.