Создание PHP TCO Calculator

Question

Я создаю калькулятор TCO. Я в состоянии получить первую часть PHP, которая отображает заданные числа в полях ввода и вычисляет переменные в конечный результат просто отлично. Вторая часть, где пользователь может изменить числа в этих входах и затем пересчитать результаты на той же странице, не работает. Вот что я сделал до сих пор:

    <?php

        // This works like a charm!

        // prefill the form inputs
        $parnum = "1000000000"; // Revenues
        $pirnum = "4.00"; // % Revenue
        $pesnum = "10.00"; // % Scope

        // calculate the form formula
        $hccput = round($parnum * ($pirnum / 100) * ($pesnum / 100));
        $hcprice_text = (string)$hccput; // convert into a string
        $tothccost = number_format($hcprice_text);
        $preput = $hccput;
        $preput2 = .535808;
        $eqdput = round($preput * $preput2);
        $eqdprice_text = (string)$eqdput; // convert into a string
        $toteqdhccost = number_format($eqdprice_text);

        // create the dynamic bars
        $toteqdhcsave = round(100 - ($eqdput / $preput) * 100);
        $toteqdhcsave2 = 100 - $toteqdhcsave;
        $eqdhcsoutput = $toteqdhcsave2;
        $tothcsave = 100;
        $toteqdhcper = 'height:' . $toteqdhcsave . '%';
        $tothcper = 'height:' . $tothcsave . '%';
    ?>

    <div class="medium-12 columns">
            <form id="hard-cost" class="medium-6 columns clearfix" action="<?php $_SERVER['PHP_SELF'];?>" method="post">
                    <h2 class="text-center">(PHP)</h2>
                    <div class="slidecontainer">
                            <div class="small-12 columns">
                                    <label>Revenues</label>
                                    <input type="number" value="<?php echo $parnum; ?>" onchange="handleChange10(this);" min="1" max="10000000000" name="parnumphp" id="parnumphp" />
                                    <label>% Revenue</label>
                                    <input type="number" value="<?php echo $pirnum; ?>" onchange="handleChange11(this);" min="1.00" max="100.00" name="pirnumphp" id="pirnumphp" />
                                    <label>% Scope</label>
                                    <input type="number" value="<?php echo $pesnum; ?>" onchange="handleChange11(this);" min="1.00" max="100.00" name="pesnumphp" id="pesnumphp" />
                                    <input type="button" value="submit" class="button blue-bg white m-bottom" name="hchnumphp" id="hchnumphp" />
                            </div>
                    </div>
            </form>
            <div class="tothc-calcphp medium-6 columns medium-centered">
                    <h4 class="text-center">Pay <span id="toteqdhcsave"><?php echo $toteqdhcsave2; ?></span>% less</h4>
                    <ul id="bars">
                            <li class="small-4 small-push-1 columns">
                                    <div id="toteqdhcper" class="bar" style="<?php echo $toteqdhcper; ?>"></div>
                                    <div class="bar-text">
                                            <h4>Cost 1:<br /> $<span id="toteqdhccost"><?php echo $toteqdhccost; ?></span></h4>
                                    </div>
                            </li>
                            <li class="small-4 small-push-3 columns">
                                    <div id="tothcper" class="bar" style="<?php echo $tothcper; ?>"></div>

                                    <div class="bar-text">
                                            <h4>Cost 2:<br /> $<span id="tothccost"><?php echo $tothccost; ?></span></h4>
                                    </div>
                            </li>
                    </ul>
            </div>
    </div>

    <?php

        // THIS ISN'T WORKING AT ALL!!!
        if(isset($_POST['hchnumphp'])){
            $parnumphp = $_POST["parnumphp"]; // Revenue
            $pirnumphp = $_POST["pirnumphp"]; // % Revenue
            $pesnumphp = $_POST["pesnumphp"]; // % Scope

            echo "parnumphp is: " . $parnumphp; // TESTING BUT IT"S NOT WORKING
            echo "pirnumphp is: " . $pirnumphp; // TESTING BUT IT"S NOT WORKING
            echo "pesnumphp is: " . $pesnumphp; // TESTING BUT IT"S NOT WORKING

            // calculate the formula
            $hccputphp = round($parnumphp * ($pirnumphp / 100) * ($pesnumphp / 100));
            $hcprice_textphp = (string)$hccputphp; // convert into a string
            $tothccostphp = number_format($hcprice_textphp); 
            $preputphp = $hccputphp;
            $preput2php = .535808;
            $eqdputphp = round($preputphp * $preput2php);
            $eqdprice_textphp = (string)$eqdputphp; // convert into a string
            $toteqdhccostphp = number_format($eqdprice_textphp);

            // create the dynamic bars
            $toteqdhcsavephp = round(100 - ($eqdputphp / $preputphp) * 100);
            $toteqdhcsave2php = 100 - $toteqdhcsavephp;
            $eqdhcsoutputphp = $toteqdhcsave2php;
            $tothcsavephp = 100;
            $toteqdhcperphp = 'height:' . $toteqdhcsavephp . '%';
            $tothcperphp = 'height:' . $tothcsavephp . '%';
        }

    ?>

    <script>
            function handleChange10(input) {
                    if (input.value < 1) input.value = 1;
                    if (input.value > 10000000000) input.value = 10000000000;
            }
            function handleChange11(input) {
                    if (input.value < 1) input.value = 1;
                    if (input.value > 100) input.value = 100;
            }
    </script>