positioning for everyone

[r3ckless]

Hey guys I'm trying to setup a custom HP HUD. I'm having trouble with placement on screen though. I'm using screenheight/width, but when I line it up perfect on my screen, its not perfect for everyone else. How would I go about doing this correctly?

This is a part of what I have:

PHP Code:

function ShowHP_Bar()
{
with (findimg(250)) {
image = "bigheart.png";
    x = screenwidth-200;
    y = screenheight-540;
    partw = 40;
    parth = 44;
    layer = 4;
   }
}