The newest ScreenRuler adds mouse tracking, helping you get precise measurements:
This is by far the most requested feature so I’m happy to finally get it done. :) It works for all metrics: pixels, centimeters, inches, picas, points, and percentage.
The arrow keys now move the ruler by 1 pixel, and Shift-ArrowKeys move it by a bigger step, which is the reverse of previous versions. I hope this makes single-pixel adjustment easier to use and more discoverable.
After some testing and feedback I’ll update the Ubuntu package.