Factory recalibration is done on an as-needed basis. When diagnostic flags begin to appear and persist even after cleaning the analyzer and verifying its settings, a recalibration is needed. Additionally, if the performance of the analyzer has degraded, a recalibration is recommended.
One performance test is to check the absolute signal strength drift over the course of 1 year. Drift of a few percent per year is normal. If the annual signal strength drift is excessive, or if the signal strength is below 0.7 when the windows are clean, a factory recalibration is needed. Furthermore, if the ratio of the CO2 to H2O signal strength is not close to one, it may also be time for a factory recalibration.