<body>
  <div id="timerDiv">
    <input type="text" id="tf1" size="6" style="text-align:center;" />
    <input type="button" id="btnStart" value="Start"
           onclick="btnStartClick();" />
    <input type="button" id="btnStop" value="Stop"
           onclick="btnStopClick();" />
   </div>
</body>