Yep. The names are not important. No link between the two. Heck, you could even do this:
class Calc {
private $num1;
private $num2;
private $cal;
public function __construct($arg1, $arg2, $arg3) {
$this->num1 = $arg1;
$this->num2 = $arg2;
$this->cal = $arg3;
}
Not recommended but it would work.
And please stop using tabs. Have your IDE expand tabs into spaces.