Speed scrollbar

The first element in the rotation panel is a scrollbar which is used to
control the apparent speed of rotation.  (In fact it sets the angle of
rotation between successive replots of the data.)

To control the scrollbar, position the cursor about where you'd like
the new speed 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
speed interactively.