Jump size scrollbar

The first scrollbar controls the tour "jump size", that is, the
distance between the starting and ending plane.  Its effect is to
control the frequency of the derivative calculations.  When the
jumpsize is large the tour is allowed to move further before a new
direction, based on the derivative, is calculated.  (This is a
primitive, manually-controlled derivative-based optimization method).

To control the scrollbar, position the cursor about where you'd like
the new jump size to be, then click the left or middle mouse button.
You can also move the cursor with the mouse button held down to adjust
the jump size interactively.