I have a list of check boxes with values. Clicking each check box, displays the sum of the checked box and the MSRP value (1000) in a div - as outlined below. Can someone explain this little snippet and why it is not working? I started hacking this snippet and it is beyond meaningful.. so be gentle.

Code HTML4Strict:
<p>MSRP: 1000</p>
<ul id="ComboOneAddonPricing">
<li><label for="addon-a">Addon One<input id="addon-a" type="checkbox" value="500"></li>
<li><label for="addon-b">Addon Two<input id="addon-b" type="checkbox" value="700"></li>
</ul>
 
<div id="comboOneSum">1000</div>
Code JavaScript:
jQuery(document).ready(function($) {
            var comboOneSum = 1000;
            $('#ComboOneAddonPricing :checkbox').click(function() {
                comboOneSum = 1000;
                $('#ComboOneAddonPricing :checkbox:checked').each(function(idx, elm) {
                    comboOneSum += parseInt(elm.value, 10);
                });
 
                $('#comboOneSum').html(comboOneSum);
            });