timerRunning=true;
function Halt() {
    if(timerRunning)
        clearTimeout(timerID)
    timerRunning = false
}
function Start() {
    if (t_time<=0) {
        Halt();
        document.getElementById("e_after").style.display = 'block';
        document.getElementById("e_before").style.display = 'none';
    } else {
        t_time = runde((t_time - 0.1), 1)
        window.document.getElementById("timer").value = t_time + ' Sekunden'
        timerRunning = true
        timerID = self.setTimeout("Start()", 100)
    }
}

function runde(x, n) {
  if (n < 1 || n > 14) return false;
  var e = Math.pow(10, n);
  var k = (Math.round(x * e) / e).toString();
  if (k.indexOf('.') == -1) k += '.';
  k += e.toString().substring(1);
  return k.substring(0, k.indexOf('.') + n+1);
}