protected function decimalValue()
    {
        $base = $this->numberSystem->getBase();
        $result = 0;

        foreach (array_reverse($this->getDigits()) as $position => $value) {
            $numberSystemPosition = $this->numberSystem->getSymbolPosition($value);
            $result += $numberSystemPosition * pow($base, $position);
        }

        return $result;
    }