public function getElapsedTime($decimals = null)
    {
        if (!$this->hasStopped()) {
            return false;
        }

        $elapsedTime = $this->_stopTime - $this->_startTime;

        if ($decimals) {
            return number_format($elapsedTime, $decimals);
        } else {
            return $elapsedTime;
        }
    }