[jQuery] Variable in :eq() with jquery.calculation

[betweenbrain]

Hi All,

I'm trying to use jquery.calculation to calculate some text inputs
versus a selected field. I'm running into an issue with using
variables to select information from the same row. Here's what I have
so far. Any help would be greatly appreciated:

<script type="text/javascript">
        $(document).ready(
                function (){
                        $("input[name^=module-]").bind("keyup", recalc);
                        $("input[name='input-positions']").bind("click", 
recalc);
                        recalc();
                }
        );

        function recalc(){
        var i = $(this)[0].rowIndex;
                $("[id=total-positions-left]").calc("avail - (used * qty)",
                        {       avail: 
$("[name='input-positions']:checked").val(),
                                used: $("[td.item-qty-pos-reqd'].eq(i)"),
                                qty: $("input[id^='module-qty'].eq(i)")
                        }),
                i = ++
                        $("#total-positions-left").text($this.sum()
                                );
                        }
        </script>