Reading gooing up and down

Have a look at my graph, it might be nothing but Im a little bit confused by the mean reading is going up and then down with about 30 mins to 60 mins between the tops and the downs. What can this be? I have 42 samples now (the answe to everything ) and it will of course smooth out when I increase it!

It looks stable for the last 3 days. Before that, was your sensor plugged in a different way? The USB serial converter chip in your sensor may not work reliably if it is plugged in to a powered USB hub instead of directly to a MB port. That is what I found with mine (different sensor but also uses USB-serial chip). Yours seemed to revive after the low/0 readings; did you have the Radmon Setting ticked for 'Using HC05 Bluetooth module'? That setting periodically resets the port.

Yes it was plugged thru an external powered USB hub before so that might have been it!Now it goes directly into my laptop again!