DesignCad allows you to zoom in/out while holding the ctrl key and rolling the mouse wheel. If the zoom command is running you can roll to zoom without holding Ctrl.

To set a zoom focus then roll-zoom here's what to do:

Hit "z" then "-" or "+" (doesn't matter if you want to zoom in or out, just hit either - or +). This issues the 'zoom window' command with 'zoom in' or 'zoom out' just before it. Click the area of focus, which would zoom in or out once while centering on where you clicked. The zoom command would now become active so you can just scroll the mouse wheel for further zooming. To refine your zoom hit + or - again and clicking on the new focus point. The screen would zoom in/out then return to the zoom window command for further wheeling. When done press esc to end the zoom command or issue another drawing command. Or you could actually click 2 points to define a window to zoom in on.