 
 import spark.components.supportClasses.ScrollBar;
 import spark.core.IViewport;
-import spark.core.ScrollUnit;
+import spark.core.NavigationUnit;
 
 //--------------------------------------
 //  Other metadata

            // implementation.
            oldStepSize = stepSize;
            stepSize = Math.abs(viewport.getVerticalScrollPositionDelta(
                (increase) ? ScrollUnit.DOWN : ScrollUnit.UP));
        }
        super.step(increase);
        if (viewport)

            // implementation.
            oldPageSize = pageSize;
            pageSize = Math.abs(viewport.getVerticalScrollPositionDelta(
                (increase) ? NavigationUnit.PAGE_DOWN : NavigationUnit.PAGE_UP));
        }
        super.page(increase);
        if (viewport)
