var resolution = get_resolution();

function get_resolution() {
   width = screen.width;

   // note that ALL resolutions are supported but only 3 resolutions are actually designed
   switch (width) {
      case 640  :	return 640;
      case 720  :	return 640;
      case 800  :	return 800;
      case 848  :	return 800;
      case 1024 :	return 1024;
      case 1152 :	return 1024;
      case 1200 :	return 1024;
      case 1280 :	return 1024;
      case 1600 :	return 1024;
      case 1680 :	return 1024;
      // if unknown resolution the default is 1024
      default   :	return 1024;
   }
}