Use the options on the View tab > Navigate panel > Zoom menu to zoom in or out of a view:
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Zoom to Box — Click and then use the left mouse button to drag a box over a section of the graphics window to zoom into the specified area. For example:
It converts this:
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Zoom box
to this:
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Zoom In — Click to zoom in to the centre of the graphics window. Click repeatedly until you achieve the desired zoom amount.
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Zoom Out — Click to zoom out from the centre of the graphics window. Click repeatedly until you achieve the desired zoom amount.
Tip: You can also resize a model by holding down the Ctrl key and the middle (or right) mouse button, and then dragging the mouse up to Zoom In or down to Zoom Out.