A working example with variable input for validating the asymptotic analysis of your algorithm:

<?php

$n = 1000; // Size of your input

declare(ticks=1);

class Counter {
    private $counter = 0;

    public function increase()
    {
        $this->counter++;
    }
    
    public function print()
    {
        return $this->counter;    
    }
}

$obj = new Counter;

register_tick_function([&$obj, 'increase'], true);

for ($i = 0; $i < 100; $i++)
{
    $a = 3;
}

// unregister_tick_function([&$obj, 'increase']);
// Not sure how to de-register, you can use static methods and members in the Counter instead.

var_dump("Number of basic low level operations: " . $obj->print());

?>

Due to an implementation bug, the declare(ticks=1) directive leaked into different compilation units prior to PHP 7.0. This is not how declare() directives, which are per-file or per-scope, are supposed to work.

Therefore there are different implementations between PHP 5.6 and the correct implementation has been added in PHP 7.0. This means the below script will return different results

#index.php

<?php

declare(ticks=1);
$count = 0;

register_tick_function('ticker');
function ticker() {
  global $count;
  $count++;
}

?>

#inc.php

<?php

$baz = "baz";
$qux = "qux";

?>

Running php index.php in the terminal gives:

    PHP 5.6 - 7
    PHP 7.0 - 5