I think a lot of it depends on where you have the hygrometer in the still air bator. I was just warming up one of mine, and had the hygrometer in the middle, the humidity was 65%. I moved the hygrometer to the side, and it is now at 50%. The air just kind of sits there, so it is hard to guess where it is accurate. It can be done, as I have duck eggs in one bator, and the humidity is a stable 70%. I have to use at least 2 wet sponges, along with the paper towel wicks and full water wells.