Preloader to play at 50% load

1

Have searched in vain to find out how to modify this code to load at the 50% or 50000 b point

can someone enlighten me

bytes_loaded = Math.round(_root.getBytesLoaded());
bytes_total = Math.round(_root.getBytesTotal());
getPercent = bytes_loaded/bytes_total;
_root.loadBar._width = getPercent100;
_root.loadText = Math.round(getPercent100)+"%";
if (bytes_loaded == bytes_total) {
_root.gotoAndStop(3);
}

thanks