index.php - Usage of class, methods

<form action="" method="post">
    <input type="number" name="num1" placeholder="Enter the first number"><br><br>
    <input type="number" name="num2" placeholder="Enter the second number"><br><br>
    <input name="calculation" type="submit" value="Calculate"><br><br>
</form>

<?php
class Calculator
{
    public function add($num1, $num2)
    {
        echo "Summation: " . ($num1 + $num2) . "<br>";
    }
    public function deduct($num1, $num2)
    {
        echo "Deduction: " . ($num1 - $num2) . "<br>";
    }
}

if(isset($_POST['calculation'])){
    $num1 = $_POST['num1'];
    $num2 = $_POST['num2'];

    if(empty($num1) || empty($num2)){
        echo "<p style='color:#ee6554'>Fields can not be empty!</p>";
    } else {
        $calc = new Calculator();
        $calc->add($num1, $num2);
        $calc->deduct($num1, $num2);
    }
}