Synchronize the contents of the open view windows, so when you track or dolly in one window the other windows move along with it.
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Choose Window Sync again to turn off synchronization.
This normally applies to the orthographic windows only (Top, Side, Back, etc.). However, it works in the Perspective window if Perspective is turned off in the Viewing Panel or ViewCube and one of the preset orthographic views (horizontal or vertical arrows) is selected.
