My long-term radiation average for my basement Geiger counter here at the Regenstein Library is 7.6uR/hr. Lately it's been elevated a touch. For the last 1372 minutes (or roughly a day), it's 7.95uR/hr. Over the last hour, it's at 8.38 (EDIT: in the space of writing this the last 60 count rate went down to 7.67. Love them statistics). All of this is so small that it doesn't matter but it's an interesting variation. Merely putting a simple aluminum can near the Geiger counter can drop the reading by 0.5uR/hr, so these changes aren't significant. I wonder if I've made some change in my office (or perhaps in the next office) that has changed the local background rate. The air is off too; perhaps that's allowing a small amount of radon to appear (which is normally non-existant in the library).
The popular Geiger Counter post. In which I graph the radiation on an airplane flight. And radon decay.