This is a n00b question!
When I slide the trigger line (up or down) on the RTB2004, a dotted (or dashed if your prefer) line shows up above and below the trigger line. This happens while the solid trigger line is being dragged and then those dotted lines disappaer once the drag is finished.
I've read the scope manual entirely and I don't see this mentioned anywhere. I'm at a loss to figure out what these lines actually mean. Also, these dotted lines don't don't show up if I turn on "HF reject".
My threshold is set to 0 and hysteresis to small - not sure if that has any connection to these dotted lines (they don't seem to expand further when hysteresis is set to large).
[edit: attached a pic to show this]