How to get there
From the Zoom submenu of the View Menu, choose Other (or type command-0).
What it does
In this dialog box, you can specify the size at which you want the score displayed on your screen, expressed as a percentage of its actual size—in other words, you can "zoom in" to magnify fine details of your score or "zoom out" if you want to see many staves at once. Note that this screen display size has nothing to do with the actual (printed) size of the music.
Tip: numbers larger than 100 will increase the size.
Tip: To change the size of the printed music, use the Resize Tool
See Also: