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