function numbersonly(myfield, e, dec){
var key;
var keychar;
if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);
if ((key==null) || (key==0) || (key==8) || 
(key==9) || (key==13) || (key==27) )
return true;
else if ((("0123456789").indexOf(keychar) > -1))
return true;
else if (dec && (keychar == ".")){
myfield.form.elements[dec].focus();
return false;
}else
return false;
}

function Vacio(NUMPER) {
   if ((NUMPER.value.length==0) ||
   (NUMPER.value==null)) {
      return true;
   }
   else { return false; }
}	

function ValidaNumper(form){
   if(Vacio(form.NUMPER)){ 
      alert('El periodo en meses es requerido') 
      form.NUMPER.focus(); 
      return false; 
   } 
return true;
 
}