What is net temperature and how do I measure it?

What is net temperature and how do I measure it?

Net temperature is calculated by deducting the internal AMBIENT temperature from the measured FLUE temperature.

Displays in either Centigrade (°C) or Fahrenheit (°F) and will display NOT FITTED if flue probe is not connected.

If an external INLET probe is used then INLET is deducted from FLUE.