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Screen Calipers
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The accurate way to measure on a screen, at any angle in pixels, inches or any unit.
Posted in the Screen Calipers Forum.
Google Earth
The Screen Protractor and Calipers will work with any application,
although applications that use motion graphics do occasionally cause
some flicker.
With Google Earth you can change the graphics options to stop the
flicker. Go to the 'Tools' menu and select 'Options...' then under
'Graphics Mode' select 'DirectX' instead of 'OpenGL'.