function alerta_centrada(object) {
  if (document.getElementById) {
    document.getElementById(object).style.visibility = 'visible';
  }
  else if (document.layers && document.layers[object]) {
    document.layers[object].visibility = 'visible';
  }
  else if (document.all) {
    document.all[object].style.visibility = 'visible';
  }
}

function imprimir_pantalla() {
  temp_version_nav = parseInt(navigator.appVersion);
  if (temp_version_nav >= 4) {
    window.print();
  }
}

function xIsNumeric(val){return(parseFloat(val,10)==(val*1));}

function checknum(ob) {
  if (!xIsNumeric(ob.value)) {
    alert('Please enter only numbers or decimal points in the '+ob.name+' field');
    ob.focus();
    ob.value='';
  }
}