When the trigger mode is in "Vertical", the trigger is given********
Okay ... I understood ALT, CHOP, ADD etc .... individually ... but what I didn't grasp is the 'implication' of them collectively ...
If I can re-state what you said ... the selection of "VERT MODE/ALT and TRIG SOURCE/VERT MODE" is the only mode that requires two sweeps (one for trace A and one for trace B) and 2 different trigger events. All the other modes only require one sweep and one trigger event.
Doing some further experimenting with this today, I am finding that the 'jitter' is substantially less when I use higher bandwidth probes, and no co-ax, no bnc t-connector etc, to connect the Calibrator signal to the 7A15A's.
So ... somehow .... maybe this second trigger event is being compromised by my low BW equipment??