I have not done any hatching yet but have spent MANY hours reading. I pulled up the LG still air manual; it doesn't state a %RH--I called customer service. Very nice to talk to but would not confirm a %RH; manual designed for everyone to use any where.
Chookschick has an incubating sheet with detail on dry incubating. THe point is to have the air cell large enough by day 18 to be effective as an air source for breathing by the chick. Then increase to 75% RH
Another poster, Cashdl, also does the dry incubation method, running at about 30% RH then increases the %RH to 65%. Both these sources report a high hatch rate repeatedly.
It is all rather confusing when other documentation(Mississippi Ste University extension) puts %RH at 55-60.
Your best bet is to find the good drawings that show the increase in air cell size at specific days of the incubation period and that will be the best judge of the level of humidity. University of Mississippi Extension documents states, " An excellent method of determining proper humidity is to candle the eggs and observe the size of the air cell. As incubation progresses, the size of the air cell increases because of the moisture loss. Humidity adjustments can be made after each candling operation."
Here is another source, I do not know if they are a credible source or not: at
www.ogppb.com they state "If the humidity in the incubator is too low or too high, the hatch will fail. When humidity is too low during incubation, the air cell will be too large at the time of hatch. The contents of the egg will be too think and stickyfor the chick to turn. THe membraine will be too tough to break. THe navel will not close properly.If the humidity in the incubator is too high during incubation, too little water will evaporate from the egg. THe aisr cell will be too small for the chick to reach during the hatching process. THe chick will either drown or the chick will be too swollen with water to turn itself within the egg. THe yolk sac will also be too large for the navel to completely close. THese problems will cause the hatch to fail. "
I will search to find some pic. If someone else has a source, feel free to post. Found a good picture/diagram that is useful, I think.
www.Poultryhelp.com/hatch.html#cond This is a Mississiippi University site.
Hope this helps you.