In Grapher 8 and above, the mouse wheel can also be used. Rotate the mouse wheel forward to zoom in, rotate the mouse wheel backward to zoom out. Press and hold the mouse wheel down to pan the view.
In older versions of Grapher (1-9), you can zoom continuously by double clicking on the zoom tool to enable persistent draw mode, clicking on your page the number of times you want to zoom in or out, then pressing ESC on your keyboard to exit the persistent draw mode. Alternatively, you can click View | Zoom | Zoom Realtime, then click and drag your mouse up on the page to zoom in or down on the page to zoom out.
Updated September 21, 2018