To meassure is to live
Why measure humidity? Simple, it affects very much how you perceive ambient temperature. So 20.0°C can seam very hot, or very cold, depending on humidity. If, and I must stress this out, IF you have a fetish for measuring things, next after temperature, humidity would be the logical choice.
That is why I got a couple of these babies: HIH4000-002 Solid-state humidity sensors. These are maintenance-free and with a hobby-level accuracy.
Give her 5Vdc, a 47K resistor and you are up and running, it does not get more simple than that. Currently measuring: 2.28V, this translate into: 46.2%Rh, this is a normal humidity, atleast around here. will drop during winter due to the fact that the air outside will be cold and when heated up, the RELATIVE humidity will drop.
For more on Relative Humidity, please see: Wikipedia page on %Rh
This was just a QaD set-up (yet it took me long enough to overcome CBA), on a long term, it will be logged somehow, I have a pretty good idea who will help me with that :-) - more to come.