What do the curved lines on the vectorscope display of color bars mean?

What do the curved lines on the vectorscope display of color bars mean?

When a color bar signal is displayed on a vectorscope the ends of the vectors are positioned in the boxes marked Red, Magenta, Blue, Cyan, Green, and Yellow. The trace lines connecting the boxes should be straight. When the lines are curved it indicates that there are timing differences between B-Y and R-Y components of the chrominance signal. This is caused by chrominance reconstruction filters rolling off the frequencies associated with the chrominance components unevenly and at an incorrect rate. A vectorscope display of a color bar test signal coming directly from a TV test signal generator will have straight lines between the ends of the vectors. When a signal is routed through a facility or is transmitted, distortions can arise that create timing differences in chrominance components that result in curved lines when displayed on a vectorscope.