function incrementa() {
  ss++;
  if(ss>59) {
    ss = 0;
    mm++;
    if(mm>59) {
      mm = 0;
      hh++;
    if(hh>23)
      hh = 0;
    }
  }
  relogio();
}

function relogio() {
  hh = hh.toString();
  hh = ('00'+hh).substr(hh.length,2);
  mm = mm.toString();
  mm = ('00'+mm).substr(mm.length,2);
  ss = ss.toString();
  ss = ('00'+ss).substr(ss.length,2);
  document.getElementById('horario').innerHTML = '<strong>'+hh+':'+mm+'</strong>';
}