Trolling speed, depending on where you are and species, is up to 3 mph for black bass, 2-3 mph for stripers.
When the boat is stopped, whether a bass is suspended or moving, it's likely to show up as a horizontal dash that blends in with debris, cover, structure. While the boat is stopped over it, if it does the moving, a line will draw on the constantly moving display. A 45 degree sloped line is almost always air bubbles that travel straight up, and at most chart speeds, that draws as a 45 degree slope. If there are many bubbles streaming out of a log then there will be one line for each bubble track, all perfectly parallel. If a bass swims up say at a 45 degree angle, the line might draw at 23 degrees from horizontal since the graph is moving constantly.
If you spook the bass by stopping over it you should see it make a sudden angled line. Bye Bass. "We stopped right over one, and he's GONE."
Jim