Humidity level is also influenced by the humidity in the room the incubator is kept in. So........ I also check the eggs by candling at 7, 14, and 20 days. Actually I usually check the air cells at about 5 days to verify it is getting larger and to see if perhaps, rarely, it is too large for the 7 day size. Candling is the best method, or weighing, that I know to verify the humidity is right. Adjusting as needed.
Here I need to add water during winter incubation; in the summer the humidity is too high naturally and I get poor rates of hatch. My best is spring when I can control the humidity--- using an LG.
Just google "air cells at 7 , 14 days" and a few graphs should pop up that you can print and look at while candling.
Good luck!