JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">

    <form action="sample2.php" id="calculator" name="calculator" method="post">
        <fieldset>
            <legend>Input</legend>
            V = <select name="V" id="V" tabindex="1" onchange="$('#calculator').submit();">

                    <option SELECTED value="1">1</option>
                    <option  value="10">10</option>
                    <option  value="100">100</option>
                   </select>
                <br />
            W = <select name="W" id="W" tabindex="2" onchange="$('#calculator').submit();">
                    <option SELECTED value="1">1</option>

                    <option  value="10">10</option>
                    <option  value="100">100</option>
                   </select>
                <br />
            X = <input name="X" id="X" type="text" tabindex="3" value="1" onChange="$('#calculator').submit();" />
                <br />
            Y = <input name="Y" id="Y" type="text" tabindex="4" value="1" onChange="$('#calculator').submit();" />

                <br />
            Z = <input name="Z" id="Z" type="text" tabindex="5" value="1" onChange="$('#calculator').submit();" />
                <br />
            A = <input name="A" id="A" type="text" tabindex="6" value="1" onChange="$('#calculator').submit();" />
                <br />
            B = <input name="B" id="B" type="text" tabindex="7" value="1" onChange="$('#calculator').submit();" />
        </fieldset><br />

        <fieldset>
            <legend>Output</legend>
            W+X+Y+Z+A+B = 6<br />
            <span style="display:none">
            shiftCatch = <input name="shiftCatch" id="shiftCatch" type="text" value="" /><br />
            captured = <input name="captured" id="captured" type="text" value="" /><br />
            recaptured = <input name="recaptured" id="recaptured" type="text" value="V" />

            </span>
        </fieldset>
    </form>

</div>

JavaScript

$(document).ready(function() {
    var elements = $("#container :input:visible");
    var n = elements.length;
    elements
    .keydown(function(event){
        if (event.keyCode == 9) { //if tab
            var currentIndex = elements.index(this);
            var newIndex = event.shiftKey ? (currentIndex - 1) % n : (currentIndex + 1) % n;
            var el = elements.eq(newIndex);
            if (el.attr("type") == "text")
                elements.eq(newIndex).select();
            else
                elements.eq(newIndex).focus();
            event.preventDefault();
        }
    }).eq(0).focus();
});