The expected precision for the half-hour average CO2 and H2O concentrations is 0.08 ppm for CO2 and 0.0008 ppt (0.8 ppm) for H2O. This is estimated as follows. The LI-840A maximum RMS noise specification is 1 ppm for CO2 and 0.01 ppt for H2O. Assuming the AP200 is configured with eight levels, it will switch to a new level every 15 s, cycling through the set of eight levels every two minutes. Each time the valves switch, the first 10 s are omitted for equilibration, and 5 s (10 samples) are included in the average. In each half-hour averaging period, each level will have a total of 150 samples (10 samples per cycle, and 15 cycles per half hour). The precision of the CO2 and H2O average concentrations can be given as the standard error of the mean. This is calculated as the RMS noise of individual samples divided by the square root of the number of samples, giving a precision of 0.08 ppm for CO2 and 0.0008 ppt (0.8 ppm) for H2O.