The value of a variable varies according to clicking side of a pop-up in netscape applicaton?

The value of a variable varies according to clicking side of a pop-up in
netscape applicaton?

We have a netscape application in which i am not able to understand the
value of x...
public void mouseUp(MouseEvent event){
if (!event.isMetaKeyDown()){
int x = event.x;
This x varies up to 200 on clicking on a pop-up's side.
Could anyone please help me to understand it. Thanks in Advance.