Fluctuating hydrometer?

[takinyan]

I bought a new hydrometer/temp gauge since my last one was stuck at 0%. The humidity the new one reads jumps all over the place though. One hour it's at 70%, next is at 100%, then down to 60%, back up to 80%.... Is this normal? Is it fine as long as it's in a good range? There is no condensation on the glass whatsoever, so I'm not sure if the humidity is actually ok at all. Here is a pic of the one I bought.

[CallaLily]

There are directions here on how to calibrate your hygrometer to make sure your readings are accurate.