The attached is a demo of a qvw I created with a slider that helps zoom in and out a form on the screen. .
The slider is linked to a variable (vZoomLevel) that on a trigger, when changes occur via the slider, calls a macro Sub Zoom, which in turn calls Sub ZoomInOut and passes to it the value of the Zoom. There is also a "reset" button to facilitate easy change back to 0 Zoom.