Yo know DC that makes a lot of sense. I've wondered the same thing myself. I'm have an hvac license and we deal with the RH factor all the time. The only true way to read humidity is the use of a device called a sling psychrometer. You take what is called a wet bulb and dry bulb reading to get humidity levels in a space to properly size an ac unit. That being said my humidity levels run a lot like what you mentioned from really high in summer to really low in winter. I actually had a reading this winter of 12% and last summer a peak of 100% outside. My actual average runs right at 66%. Patrick