Quantum Data 801GC, 801GF, 801GX Owner's And Programmer's Manual page 110

TV Vectorscope signature of the TVBar_75 Image
using NTSC color encoding on the 801GX.
TV Vectorscope signature of the TVBar_75 Image
using PAL color encoding on the 801GX.
There are twice as many points as NTSC because the
color sub-carrier phase is reveresed every other scan line.
4-72 Model 801GC, 801GF & 801GX¥Rev. X1
Chapter 4: Built-In Images