I have a PHP script which moves a small graphic around on a larger background graphic, with "go" and "no go" areas. It works nicely on my computer, but when I try it out on another computer, with the same screen resolution, the smaller graphic is out of alignment with the background graphic. That is, it can move into some "no go" areas, and can't get into some "go" areas.

Any explanation for this that may help me to recode my script to take account??