On certain images, you may want to zoom in really close to do some detail work, but at the same time, you might need to see how the overall image looks. To solve this problem you can open the same document in two windows and put them side-by-side in two different zoom levels.
To do this, (with your document open) go to Window > Arrange > New Window for [file name of your document], which will open up a second window for the original document. Then go to Window > Arrange > 2-Up Vertical to place the two windows side-by-side. You can then zoom to different levels on each. Whatever adjustments you make to one window will be reflected on the other.
You can then zoom to different levels on each. Whatever adjustments you make to one window will be reflected instantaneously on the other.
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