Have you ever felt like the middle mouse wheel zoom is too fast or too slow when drawing? It can depend on the scale of the drawing and objects you are working on, or perhaps even your mood. This speed of the zoom in and out is controlled by a system variable named ZOOMFACTOR. The default of the system variable ZOOMFACTOR is 60. You type ZOOMFACTOR and then change the value.
This is another one of those little settings that allow you to make GstarCAD more tailored to your use whether you like warp speed zooms or turtle slow zooming with the mouse wheel.