как сделать чтобы калькулятор считал автоматически без нажатия на кнопку

<Script lang="JavaScript">
function calculator(form) {
c1 = eval(form.c1.value);k1 = eval(form.k1.value);c2 = eval(form.c2.value);
k2= eval(form.k2.value);c3 = eval(form.c3.value);k3 = eval(form.k3.value);
c4 = eval(form.c4.value);k4 = eval(form.k4.value);c5 = eval(form.c5.value);
k5 = eval(form.k5.value);c6 = eval(form.c6.value);k6 = eval(form.k6.value);
c7 = eval(form.c7.value);k7 = eval(form.k7.value);c8 = eval(form.c8.value);
k8 = eval(form.k8.value);c9 = eval(form.c9.value);k9 = eval(form.k9.value);
c10 = eval(form.c10.value);k10 = eval(form.k10.value);
c11 = eval(form.c11.value);k11= eval(form.k11.value);
c12 = eval(form.c12.value);k12 = eval(form.k12.value);
c13 = eval(form.c13.value);k13 = eval(form.k13.value);
c14 = eval(form.c14.value);k14 = eval(form.k14.value);
s=c1*k1+c2*k2+c3*k3+c4*k4+c5*k5+c6*k6+c7*k7+c8*k8+c9*k9+c10*k10+c11*k11
+c12*k12+c13*k13+c14*k14;
form.total.value = s;
}
</script>
 
 
<form> 
<table style="font-size: 13px; line-height: 4px; font-family: Verdana, Arial, sans-serif;" height="251" width="855">
<tbody>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c1"> <option>1945</option> </select> * кол-во<select id="k1"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c2"> <option>500</option> </select> * кол-во<select id="k2"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c3"> <option>600</option> </select> * кол-во<select id="k3"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c4"> <option>250</option> </select> * кол-во<select id="k4"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c5"> <option>300</option> </select> * кол-во<select id="k5"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c6"> <option>500</option> </select> * кол-во<select id="k6"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c7"> <option>600</option> </select> * кол-во<select id="k7"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
<td><span style="color: #ffff00;"><input onclick="calculator(this.form)" value="Рассчитать" type="button"></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c8"> <option>700</option> </select> * кол-во<select id="k8"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
<td style="text-align: left;"><span style="color: #ffff00;"><em><strong>Результат</strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c9"> <option>800</option> </select> * кол-во<select id="k9"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
<td><span style="color: #ffff00;"><strong><input name="total" type="text"> </strong></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c10"> <option>600</option> </select> * кол-во<select id="k10"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
<td><span style="color: #ffff00;"><input value="Сброс" type="reset"></span><br><br><span style="color: #ffff00;"><em>&nbsp;</em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c11"> <option>720</option> </select> * кол-во<select id="k11"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c12"> <option>840</option> </select> * кол-во<select id="k12"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c13"> <option>960</option> </select> * кол-во<select id="k13"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
<tr>
 
<td><span style="color: #ffff00;"><em><strong><select id="c14"> <option>150</option> </select> * кол-во<select id="k14"> <option>0</option> <option>1</option> <option>2</option><option>3</option> <option>4</option> <option>5</option><option>6</option> <option>7</option> <option>8</option><option>9</option> <option>10</option> <option>11</option></select></strong></em></span></td>
</tr>
</tbody>
</table>
</form>

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
<script>
onload = function ()
{
var nums = [1945, 500, 600, 250, 300, 500, 600, 700, 800, 600, 720, 840, 960, 150];
var obj = document.getElementById ('myTBL'), str = nums.length;
for (var j = 0; j < str; j++)
   {
   var ro = obj.insertRow (-1);
      var ce = ro.insertCell (-1); ce.innerHTML = nums [j];
      with (ce.style) textAlign = 'right', padding = '2px 5px';
 
      var ce = ro.insertCell (-1); ce.innerHTML = 'x'; 
      with (ce.style) textAlign = 'center', padding = '2px 5px';
 
      var ce = ro.insertCell (-1);
      with (ce.style) textAlign = 'right', padding = '2px 5px';
      var sel = document.createElement ('select'); sel.dir = 'rtl';
      for (var k = 0; k < 12; k++)
         {
         var opt = document.createElement ('option');
         opt.text = k; sel.options.add (opt);
         }
      sel.onchange = function calc ()
         {
         var obj = document.getElementById ('myTBL'),
             rws = obj.rows, lr = rws.length - 2,
             sls = obj.getElementsByTagName ('select');
         for (var rez = j = 0; j < lr; j++)
            rez += sls [j].selectedIndex * rws [j].cells [0].innerHTML;
         obj.getElementsByTagName ('input') [0].value = rez;
         }
      ce.appendChild (sel);
   }
var ro = obj.insertRow (-1);
   var ce = ro.insertCell (-1); ce.colSpan = 2; ce.innerHTML = 'Ðåçóëüòàò:'; with (ce.style)
   padding = '10px 5px', fontWeight = 'bold', borderTop = '2px solid #000';
   var ce = ro.insertCell (-1); ce.vAlign = 'bottom'; with (ce.style)
   padding = '10px 5px', textAlign = 'right', borderTop = '2px solid #000';
   var inp =  document.createElement ('input'); inp.readOnly = true; inp.value = 0;
   with (inp.style) width = '70px', textAlign = 'right'; ce.appendChild (inp);
var ro = obj.insertRow (-1);
   var ce = ro.insertCell (-1); ce.colSpan = 3; with (ce.style)
   padding = '10px 5px', textAlign = 'right', borderTop = '1px solid #000';
   var inp =  document.createElement ('input'); inp.type = 'button'; inp.value = 'Ñáðîñ';
   inp.onclick = function ()
      {
      var obj = document.getElementById ('myTBL'),
          sls = obj.getElementsByTagName ('select'),
          ls = sls.length;
      for (var j = 0; j < ls; j++) sls [j].selectedIndex = 0;
      obj.getElementsByTagName ('input') [0].value = 0;
      }
   ce.appendChild (inp);
}
</script>
</head>
<body>
<table id="myTBL" cellspacing="0" cellpadding="0"></table>
</body>
</html>