Screen calibration test page
To use it, download the zip file, uncompress it (on your desktop for instance), open the file 'screen-calibration.html' with your browser, then follow the instructions.
Courtesy of Erick Seban-Meyer
The original page (in french) is here : [link]
PS : As my english is ... hmm how to say ?... don't hesitate to tell me any typo thanks !