Building a forced air incubator, first timer

[chickenhobby1]

I have had chickens a long while but I am now just starting to build a diy incubator. My question is what are some recomended and humidity levels? I have done a lot of research and the temp needs to be 99.4 F-100.2 but what I have found is a lot of people and websites saying a lot of different humidity levels from 35 to 65% on day 1-18 and 70-80% from day 18 to hatch. I am wondering the humidity seems to be my question? Where should the humidity be for chickens?

 

[Flawedatdesign]

I run mine between 40-50% from day 1 to 18. Day 18 I raise it to 70% plus.

 

[rebel yell]

mine runs about 35-40 the first 18 days & then I up it to 60-65%