confused? incubating duck eggs and humidity

[lnp3]

So i just started doing this, and I have been trying to read online about the different humidity and temperatures that the duck eggs need to be at, and now i'm just conufsed lol. I bought a thermometer that also measures humidity, and am going to use that in my incubator. However, i have read on different sites, one being the metzer farms website, that the humidity in the incubator should be at 86. On another website, the Cornell university college of veterninary medicine, it says that the relative humidity should be at 55. Is there a difference if you are using the "wet bulb" method? also, what is the wet bulb method?? so confused, and i should be getting my eggs tomorrow!! if anyone could help me i'd really appreciate it!