one distinctive aspect of the LI-6400 is that the co2 and h2o infrared analyzers are located in the sensor head instead of the console. the minimum distance between the leaf atmosphere and the analyzer allows fast measurements of both co2 and h2o , which can thus be displayed in real time. the two infrared analyzers, whose reading are averaged,measure the absolute co2 and h2o concentration at both the reference flow and the sample itself. co2 and h2o are discriminated from other IR-absorbing gasses by making reference measurements at 4.1 microns(co2) and 2.40 microns. thus,the analyzers avoid background noise.