Wiki article question: CO2_Sensor_SKU:SEN0159

This is a question about information on https://www.dfrobot.com/wiki/index.php?t ... KU:SEN0159
Q3. How to know the voltage of the output of the sensor in volts when the concentration of CO2 is *ppm?
A. You can use a Voltage Metre to test the module's output voltage from PH2.0-3P connector. Or you could also use Arduino to read its voltage. After you got the voltage, you can divide it by the module's gain, that is 8.5 in the example2

Which module is meant in "by the module's gain" ? The Arduino board or the CO2 sensor board?

Thanks!