anchor.diff:      N = round(S#state.n_events * Pos / Range),
       Diff = 
   	case N - event_pos(S) of
  -	    D when D < 0 -> D  - 1;
  -	    D            -> D  + 1
  +	    D when D < 0 -> D;
  +	    D            -> D
   	end,
       S2 = scroll_changed(S, Diff),
       noreply(S2);
  
positive.code: 		    scroll_first(S);
  		last ->
  		    scroll_last(S)
  	    end;
  	true ->
  	    %% Down
  	    OldPos = event_pos(S),
  
negative.code: 	    PixelsPerEvent = Range / EventsPerPage,
  	    Share = EventsPerPage / N,
  	    wxScrollBar:setScrollbar(ScrollBar,
                                       trunc(EventPos * Share * PixelsPerEvent),
  				     round(Share * Range),
  				     Range,
  				     round(Share * Range),
  