This is a bit of a gotcha for young players in the Javascript game. You have a web page with a DIV which you fill dynamically with, let’s say, 5 IMG elements. How do you get the width of the DIV? You can try
document.getElementById('divId').width
but it will do you no good. The answer, use
document.getElementById('divId').offsetWidth
Here’s a handy guide when it comes to DHTML element position and locations.