      *  @see mx.components.baseClasses.FxTrackBase#setValue()
      *  @see mx.core.IViewport
      *  @see mx.core.IViewport#verticalScrollPosition
-     *  @see mx.core.IViewport#verticalScrollPositionDelta()
+     *  @see mx.core.IViewport#getVerticalScrollPositionDelta()
      */
     override public function step(increase:Boolean = true):void
     {
         if (!viewport)
             super.step(increase);
         else
-            updateViewportVSP((increase) ? Keyboard.DOWN : Keyboard.UP);
+            updateViewportVSP((increase) ? ScrollUnit.DOWN : ScrollUnit.UP);
     }
     
     /**

     *  change the vertical scroll position for page up or page down by 
     *  scrolling the viewport.
     *  This method calculates the amount to scroll by calling the 
     *  <code>IViewport.verticalScrollPositionDelta()</code> method 
     *  with either <code>flash.ui.Keyboard.PAGE_UP</code> 
     *  or <code>flash.ui.Keyboard.PAGE_DOWN</code>.
     *  It then calls the <code>setValue()</code> method to 

     *  change the vertical scroll position for line up or line down by 
     *  scrolling the viewport.
     *  This method calculates the amount to scroll by calling the 
     *  <code>IViewport.getVerticalScrollPositionDelta()</code> method 
     *  with either <code>flash.ui.Keyboard.RIGHT</code> 
     *  or <code>flash.ui.Keyboard.LEFT</code>.
     *  It then calls the <code>setValue()</code> method to 
