The EFF is a calculated figure; this figure is derived from the CO₂ and the temperature reading. If one or both of the readings are missing, the EFF will display ----.

If no temperature is displayed this could indicate a damaged thermocouple in the sample probe or the probe is connected the wrong way round.

NOTE:  In most analysers, CO₂ is a calculated figure from the O₂ measurement and will only appear when CO₂ is above 2% and O₂ is less than 18%.