The reading is in CCs of volume. The main thing is that however you read it, returning it to the same orientation will get you back to where you were (+/- any change in powder packing).
If using it as a bench measure, put a piece of paper under it to catch any powder leakage. DO NOT tighten the tension while there is powder in the measure, as you will only be trapping kernels of powder between the two conical sections. When done, disassemble and clean if it leaked.
I have found it to be an excellent powder measure, if you don't get all hung up on any leaking powder (though, while it is "breaking in" and leaking small kernel powder, I certainly would not use it on a progressive or turret press).
It feels like crap, but throws very consistent charges--and that is REALLY all you need.