It is possible to zoom in and out by holding the Control key and rotating the little ball on the mouse.
If someone zooms in so far that the work station is unusable follow these steps:
1. try to zoom out by holding the Control and turning the mouse ball
2. if that does not work, use the following key combinations:
"alt" + "command" + "8" toggles the Zoom in/out feature on / off
"alt" + "command" + "-" zoom out
"alt" + "command" + "=" zoom in