public function temperatureInCelsius($temperature, $serial_number = NULL) {
        $serial_number = $this->getDefaultSerial($serial_number);
        $temp_scale = $this->getDeviceTemperatureScale($serial_number);
        if ($temp_scale == 'F') {
            return ($temperature - 32) / 1.8;
        }
        return $temperature;
    }