From Field Precision:
The Field Precision Universal Scale is a high-accuracy spatial measurement system for any information that can be displayed on a computer screen: graphs in reports and publications, drawings, medical images and photographs. With the program, you can:
1) Create movable screen rulers precisely calibrated to images with a choice of colors and transparency.
2) Save and reload rulers for standard measurements.
3) Easily measure points on graphs, even with rotations and distortions.
4) Find coordinates and dimensions of mechanical drawings and diagrams.
5) Quickly digitize graphed curves.
6) Transfer numerical information in CSV (comma-separated variable) form to other applications via the clipboard or data files.