I ordered a separate hygrometer too. I found a pretty small one that fits inside. If you have 7 eggs in there to start, there really isn't any room for the hygrometer with the eggs on the turner. What I would do (though I was incubating silkie eggs & they're smaller) is wait for the turner to spin, then quick slide the hygrometer in between the eggs. After 1/2 hour or so I would read it, then take it back out before it spun again. I did that every day or two for the first week. After the first week, if I have a quitter/dud egg, I take that out and put the hygrometer in that space. The brinsea mini advance tends to hold humidity pretty well (for me at least).
Most people just tend to trust the brinsea... but I like having a general idea of the readings.