Using the Slider

  The slider is the rectangle that appears in the scroll bar.  The
  size of the slider indicates how much of the data appears on
  the screen.  For example, if the slider takes up 10 percent of
  the scrolling region, only 10% of the data is displayed in the
  window.

  To move quickly through the data, move the pointer to
  the slider.  Press MB1, and drag the slider up and down
  through the scrolling region.  When you release MB1, the
  information from the position in the data indicated by the
  slider is displayed in the window.