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%.