Editing : Edit Modes and Tools : Zoom Buttons : Additional Zoom Key Commands

Additional Zoom Key Commands
To return to the previous zoom level, do one of the following:
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Alt-click (Windows) or Option-click (Mac) any of the Horizontal, Audio, or MIDI Zoom buttons.
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Press Control+Alt+E (Windows) or Command+Option+E (Mac).
To zoom in horizontally on the Edit selection without affecting vertical zoom:
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If the selection contains MIDI notes, the selected MIDI notes are vertically scrolled to show in tracks as necessary.
To zoom in horizontally on a selection without affecting vertical zoom or scrolling, do one of the following:
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Press Alt+Start+F (Windows) or Option+Control+F (Mac).
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Press Control+Start+] (Windows) or Command+Control+] (Mac).
To zoom horizontally to show the entire session, do one of the following:
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Audio waveforms revert to the default vertical zoom; on tracks set to Notes view, MIDI notes zoom vertically to show all notes in the track (same as the vertical zoom in Clips view); and the Tempo Editor zooms vertically to show all tempo events.
To zoom horizontally to show the entire session without affecting vertical zoom or scrolling, do one of the following:
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Press Alt+Start+A (Windows) or Option+Control+A (Mac).
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Press Control+Start+[ (Windows) or Command+Control+[ (Mac).
To set horizontal zoom to “overview scale” (256 samples per pixel):
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