Use the "Open in new window" button in the top-left of the Probe Watch Window. This will open a single, small window that only contains the value of the probe. Once the new window is open, just minimize the Probe Watch Window.
Or, meet the new style half-way and click the "Hide probe display" of the top-right corner, then left-click and drag the "Last Updated" column off screen; this will give you a reduced version of the new Probe Watch Window.
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Matt Kirk
Inventor of ImageJVI