I was thinking, when comparing two sectors, or even laps, the way scrubbing currently works is that the cursor is fixed in the middle of the screen, while you move the distance/time left and right with your finger.@aol
Have you considered providing the opposite way in some situations, where the data is "fixed" on the screen, and you move the cursor around instead?
Examples I can think of where this might useful are:
a) landscape mode, where the whole lap can fit on the screen
b) reviewing a short-ish section of a lap, where the horizontal zoom level allows fitting all/most of the data on one screen
Alternatively, you could even make data and the cursor draggable separately with some smart UI.
For example, the cursor could have a "handle" you can drag it with, and dragging anywhere else drags the data instead.