public function gunningFogScore($strText = false)
    {
        $strText = $this->setText($strText);

        $score = Maths::bcCalc(
            Maths::bcCalc(
                Text::averageWordsPerSentence($strText, $this->strEncoding),
                '+',
                Syllables::percentageWordsWithThreeSyllables($strText, false, $this->strEncoding)
            ),
            '*',
            '0.4'
        );

        if ($this->normalise) {
            return Maths::normaliseScore($score, 0, 19, $this->dps);
        } else {
            return Maths::bcCalc($score, '+', 0, true, $this->dps);
        }
    }