function charts(){
chartsWindow = window.open("charts.php","charts","scrollbars=yes,width=740,height=720");
}

function specs(){
specsWindow = window.open("cylinder_specs.php","specs","scrollbars=yes,width=640,height=580");
}

function renew(){
renewWindow = window.open("renew.html","renew","left=100,top=0,screenX=100,screenY=0,width=793,height=706,scrollbars=no");
}