function calcula() 
{ 
 hoy = new Date(); 
 hasta = new Date("November 12, 2011 09:00"); // Cambiar aquí el valor de la fecha y hora elegida. 
 DD = (hasta - hoy) / 86400000; 
 hh = (DD - Math.floor(DD)) * 24; 
 mm = (hh - Math.floor(hh)) * 60; 
 ss = (mm - Math.floor(mm)) * 60; 
 document.getElementById('cuentatras').innerHTML =  "<big>"+Math.floor(DD)+"</big>" + "<small>D<\/small> " + "<big>"+Math.floor(hh)+"</big>"  + "<small>H<\/small> " + "<big>"+Math.floor(mm)+"</big>"  + "<small>M<\/small> " + "<big>"+Math.floor(ss)+"</big>"  + "<small>S<\/small> ";
 if (hasta < hoy) 
 { 
  document.getElementById('cuentatras').innerHTML = "Autosa-Tormes"; 
  cleartimeout(tictac); 
 } 
 else tictac = setTimeout("calcula()",1000); 
}