You have the option to toggle the behavior of the IntelliMouse wheel by either scrolling up and down a drawing page, or zooming in and out of a drawing page.
Toggle Refers to optional functionality. A lot of commands can be toggled on or off with check boxes or option buttons, as well as buttons on a toolbar. In this case, the Microsoft IntelliMouse can toggle between scrolling vertically through a document, or zooming in and out of a document by the use of the CTRL key and the mouse wheel.
To scroll up or down or zoom in and out of a drawing page, do the following:
To scroll up a drawing page, rotate the IntelliMouse wheel forward. To scroll down, rotate the Intellimouse wheel backward. ...