Taken to school again: I have been wearing my new dive compass to get used to its functions, and was worried that it had a small bubble of air, worried again that the bubble was growing in size, and worried a third time that "north" was whatever direction I happened to be driving. Of course, I then realized the air bubble was useful in literally telling which way was up [not always obvious underwater], the bubble size changed with barometric pressure, as the storms moved through, and the compass was attracted to the engine of the vehicle.