"Animated Zooming" governs the behavior of yEd's "Zoom In", "Zoom Out", "Reset Zoom", and "Fit Content" actions.
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If "Animated Zooming" is disabled, these actions will change the zoom factor in the editor area in one frame.
If "Animated Zooming" is enabled, these actions will use a smooth animation to change the zoom factor.
To understand the difference in behavior, create a diagram with one node, click reset zoom (the third button shown above), zoom out several steps (the second button shown above), then click reset zoom again.