If you use a line, make sure it is the right length (i.e. do not confuse
diameter with radius).

The thing with the regulations is that you need not declare which one of
the observation zone types you use, just the location. As long as you
actually use a valid one, the performance will count. But to do this,
you will probably have to set your PDA to the OZ of your preference.

There are a number of other gotchas in the regulation, however,
especially regarding the declaration (glider identification and so
forth), official observer etc so I suggest you spend some time with the
regs to avoid grief after you have made a significant effort in flying
the 1000k.

Alexander