<script type="text/javascript">
  function calculateErgebnis() {
    var weight = document.getElementById('x_weight').value;
    var height = document.getElementById('x_height').value;
    document.getElementById('x_result').value = Math.round((weight / height));
  }  
  </script>

<input type="text" name="x_weight" id="x_weight" onkeyup="calculateErgebnis();" value="0" />
<input type="text" name="x_height" id="x_height" onkeyup="calculateErgebnis();" value="0" />
<input type="text" name="x_result" id="x_result" disabled="disabled" />

    <script type='text/javascript' src='http://www.google.com/jsapi'></script>
    <script type='text/javascript'>
      google.load('visualization', '1', {packages:['gauge']});
      google.setOnLoadCallback(drawChart);
      function drawChart() {
        var data = new google.visualization.DataTable();
        data.addColumn('string', 'Label');
        data.addColumn('number', 'Value');
        data.addRows(1);
        data.setValue(0, 0, 'Test');
        data.setValue(0, 1, 22);


        var chart = new google.visualization.Gauge(document.getElementById('chart_div'));
        var options = {width: 150, height: 150, redFrom: 25, redTo: 30,
            yellowFrom:15, yellowTo: 18, greenFrom: 18, greenTo: 25, minorTicks: 5, max: 30, min: 15};
        chart.draw(data, options);
      }
    </script>

    <div id='chart_div'></div>