Well it can depend on several factors, like if the climate where you live is super dry, you are going to have to raise the humidity more, and not so much if you live somewhere really wet, some people do dry incubation where they don't add any water until lockdown. I've heard so many different opinions on this but I think right around there should be good. I personally keep mine around 45% and then bring it to about 70% at lockdown. Somebody told me I had it too high even at that too and to stay around 30% but about 45 works for me. I mean you can experiment and see what works for you. One hatch I added to much moisture and my hatch ended up like Sabrina's, three chicks did hatch out of 8 eggs but the rest look like they drowned or something and were huge! And the egg was super wet inside. I don't know if there is one perfect humidity. Not that I have found so far, but a lot of places say exactly what you said 45-50%. Also you need to make sure you calibrate your thermometer and hygrometer every once in a while to make sure they are still accurate. sorry this is so long and wordy, but I hope it helps.
Edited by Lil Peeps - 4/19/16 at 2:33pm