function numbersOnly(myfield, e)
{
   if (myfield.length ==0)
      myfield.value=0;  
   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==44) || (key==46) || (key==27))
      return true;
   else if ((("0123456789").indexOf(keychar) > -1))
      return true;
   else
      return false;
}

function change_medida(form) 
{
   form.submit();
}