I find the following in the documentation:
To zoom horizontally Do one of the following:
Click the horizontal zoom buttons to zoom in or out by a fixed percentage each time you click.
Drag the horizontal zoom fader to zoom in or out by the amount you drag.
Hold down the CTRL key and press the right arrow key (to zoom in) or the LEFT ARROW key (to zoom out).
Point the mouse pointer at the top half of the Clips pane or Piano Roll view time ruler, then drag up/down.
To zoom vertically do one of the following:
Click the vertical zoom buttons to zoom in or out by a fixed percentage each time you click.
Drag the vertical zoom fader to zoom in or out by the amount you drag.
Hold down the CTRL key and press the UP ARROW key (to zoom out) or the DOWN ARROW key (to zoom in).
Point the mouse pointer at the top half of the Clips pane or Piano Roll view time ruler, then click with the right mouse button and drag up/down.
To zoom into a selected area use the Zoom tool to drag-select an area of a clip or clips that you want to zoom to.
To activate the Zoom tool, hold down the Z key. When you release the mouse, the area you selected expands to fill the Clips pane window.
Zoom command keyboard shortcuts:
To do this, use this shortcut
Zoom in vertically - CTRL+DOWN ARROW
Zoom in horizontally - CTRL+RIGHT ARROW
Zoom out vertically - CTRL+UP ARROW
Zoom out horizontally - CTRL+LEFT ARROW
Undo Zoom - ALT+Z
Redo Zoom - ALT+SHIFT+Z
Turn On Zoom tool - Hold down Z
Fit project to window - SHIFT+F
Fit tracks/buses to window - F
Full Screen mode - F11
To zoom using the mouse wheel (Fast Zoom) - Hold down the ALT key and roll the mouse wheel forward to zoom in, backward to zoom out.
Hold down ALT+SHIFT to intensify mouse wheel zoom effect.
Hold down ALT+CTRL to adjust track scale (Track View Clips Pane only)
To select Fast Zoom options
1. Click the Track view Options menu and choose Zoom Options.
2. Select the intensity of the Zoom effect in Zoom Factor by using the spinners or manually entering a value.
3. Select the vertical and horizontal Zoom focus.
4. Check or uncheck Simultaneous Vertical and Horizontal Zoom.
The default is for Simultaneous Vertical and Horizontal Zoom to be checked. If you uncheck it, Fast Zoom exhibits the following behaviors.
ALT+Mouse Wheel zooms vertically
ALT+SHIFT+Mouse Wheel zooms faster vertically
CTRL+ALT+Mouse Wheel zooms horizontally
CTRL+ALT+SHIFT+Mouse Wheel zooms faster horizontally
5. Click OK.
I hope that helps,
Bob Bone