How are the dimensions of the vectorscope targets defined?

How are the dimensions of the vectorscope targets defined?

In NTSC: the small (inner) targets are defined by +/- 2.5 degrees and +/- 2.5 IRE; the large (outer) targets are defined by +/- 10 degrees and +/- 20 IRE.

In PAL: the small (inner) targets are defined by +/- 3 degrees and +/- 5%; the large (outer) targets are defined by +/- 10 degrees and +/- 20%.

All amplitudes are with respect to the nominal color vector length (amplitude) for the vector which strikes that target. That's why the targets are different sizes depending on how far away they are from the center.