datasheet 3.3.5 is the formula to calcualte the res_heat_x value which used to generate the desired temperature.
This is related to the heat plate operation to achive certain temperature.
then gas register is different part to change according to the VOC component.
This gas resister will vary becasue of the combination of [duty-cycle & heater temperature] which defines a certain equilibrium between the surface state and the ambient air
