public function __construct($a, $b)
    {
        $this->_a = $a;
        $this->_b = $b;
    }
    public function add()
    {
        return $this->_a + $this->_b;
    }
    public function subtract()
    {
        return $this->_a - $this->_b;
    }
    public function multiply()
    {
        return $this->_a * $this->_b;
    }
    public function divide()
    {
        return $this->_a / $this->_b;
    }
    public static function myconst()
    {
        return self::MYCONST;
    }
}
echo Calculator::myconst();
// displays 6
// while this also works, you should *not* do it
//$mycalc = new Calculator(12, 6);
//echo $mycalc->myconst();