Zoom In, Zoom Out

These buttons zoom in and out by one zoom level. Usually you will rather use the zoom slider in the main program window than these menu buttons, but the menu buttons provide keyboard shortcuts to zoom (Ctrl-Up and Ctrl-Down), which you will appreciate if you are keyboard guy. Unfortunately, IDL doesn't allow the shortcuts Ctrl-Plus and Ctrl-Minus, which are kind of standard for zooming (e.g., in Illustrator).