I've been looking at some France VFR charts I bought a while ago, and I noticed that some of the altitude boundaries for airspaces are written with no firm upper limit, just a plus. For example:
It's pretty clear that 3000MSL is where the lower boundary of the airspace begins, but how does one determine the top? The legend says that this marking would mean from 3000 to above 5000MSL or 2000AGL, but it doesn't say anything about what the upper limit actually is. So how does one know?