Is it made by Miller? With the digital readout? Looks kind of like this?
If it is, I'd stop worrying so much, the humidity readout on those DO NOT EVER read accurately, at least not for long. The electronics get a whiff of moisture the very first time it is used, and never give you an accurate readout again. Just go with room humidity. Chicks are tough, you've got a bit of wiggle room. I use one of these, it's an awesome beginner unit! I don't even trust the temperature though, and for me the probe has to be in a VERY specific spot, and NOT on top of the eggs, to affect the heater properly and to get good results. But I'm...a bit anal...LOL I maybe obsess a bit. Stress a lot. Check readouts 12 times a day. I turn by hand, so I candle a LOT. I used to do it every night, but now I'm confident enough to only candle every few days lol. I figure, hey, I'm handling the eggs anyway, why not? It's served me well--I can now identify an early quitter before they're dead, and remove it before it contaminates any eggs it's touching, in theory. Obviously, a turner would prevent contamination of that sort, since the eggs don't touch each other, but I've never used one, and I'm not sure I would want to, since some eggs I incubate like Muscovy, do better with less frequent turnings.
Candle, candle, candle. You will learn as you go. It's helpful to mark the air cell and track it's shrinkage by marking it again every few days. By hatch day, it should be taking up almost 1/3 of the egg at the fat end. Some people track by weighing their eggs--they lose weight as incubation progressses, and at hatch time, a healthy chick in an egg will have lost what feels like almost half the weight the egg weighed initially, but will actually be only about 15%.
Shuffle the eggs about the incubator every time you turn the eggs so none stay in "hot" or "cold" spots for very long. I personally do this by taking the first 4 or 5 eggs from the top left out, rolling the remaining row to the left, and adding the next row up (turning as I go) until I put the ones I removed on the bottom right and closing it up again.
Most of Ontario is VERY humid, at least 10 out of 12 months a year. Still-air incubators do NOT remove loads of moisture from eggs. In my limited experience, a little less moisture is better than a little more. I never use a dehumidiier, or use air conditioners, so I never have to add water, EVER. If you think broody hens do it better, well I can tell you that last year, they didn't. Chicks drowned or suffered heart failure still in the eggshell. Wet year. "Dry" chicks stand a chance, but wet ones die or hatch with all sorts of horrific anomalies or sickly, and then die.
But, you can obsess and fine-tune, later. What are you waiting for? Throw some eggs in there and get to it! Failures are AWFUL, and guilt-inducing, but there's really no other way to do it, than get your hands dirty with your first hatch. Or your fifty first. I hatched eggs for three or four years using nothing but an old-school oil-lamp: after that, a styrofoam incubator might as well be heaven :-D
If, down the road, you decide this way is too much for your heart, you can invest $$$ in a Brinsea or a cabinet incubator with a humidity pump. Set it and forget it. But, personally, I haven't invested because I'm (anal) still learning as I go and even a single failed egg is a learning experience for me. I've had hatches ranging from 30% to 100%, and some have been heartbreaking. 90% of the ones that have been heartbreaking have been because the humidity was too high. Others were high temperature spikes. Again, a little less is better than a lot more.
The bad ones are mitigated by the good. 3 weeks under heat and tender care, and you have live babies! What a miracle is that?! You can literally take a breakfast egg, stick it under a light bulb or over top of a candle flame, and three weeks later have a live peeping chick looking o you to feed it. How cool is that??