Brinsea Mini Advanced and humidity measurement question

I have never incubated eggs before and I finally got my incubator (no eggs yet). I keep reading where the weighing of the eggs is a good indicator of humidity but then I read about getting a hygrometer for humidity but I don't see how you use a hygrometer with the Mini, I mean, does it go inside? Is there a wire that goes inside? Obviously, I am confused

I was looking at this one: http://incubatorwarehouse.com/incubator-thermometer-hygrometer.html but obviously have no idea what to do with it or do I even need it? This Mini does not have humidity control just auto turn and temp control. I am so excited about this new venture and have tried to contact Buc-a-Buc Farm to get some eggs since she seems so highly rated, so I have time to order this if you experts out there think I should have it, because I haven't heard from her yet.

Well since I can't find an answer I decided to buy a hygrometer from Wal-Mart and just check the humidity before setting the eggs for a guide/general idea of what it is running and then use the weight method and watch the air cells closely. Then I can use the hygrometer for the room in any case.

Thanks so much for answering. I did buy a small one from Wal-Mart and calibrated it according to instructions on the forum. It runs about 2% high so I stuck it in the incubator and with 1 pot filled it runs at 47% with the temp at 99.5, steady there all day. I will need eventually to find a smaller size one though so I will check the cigar shops. This one is not terribly huge but it really doesn't fit well inside the Mini so I won't be able to check with any eggs in the incubator at all. I will have to weigh them. I ordered some eggs from My Pet Chicken (Buc A Buc was out) and they should arrive this week sometime. Now that "this week" is here, I am so nervous...:) lol