The non-linear response function of the Electron Capture Detector (ECD) to N2O and SF6 will be determined on a weekly basis using calibrated primary reference gases on the NOAA2006A scale for N2O and NOAA2006 scale for SF6 which are produced and calibrated at MPI-Jena. The range of concentrations in the primary reference gases is 314.1 ppb to 345.3 ppb (5 cylinders) for N2O and 7.5 ppt to 15.9 ppt (5 cylinders) for SF6. Instrument repeatability will be assessed by calculating the deviation in concentration of the working standard from the bracketing two working standards as the concentration of this is known and will be determined at the same time as the non-linear response function. The accuracy of the system will be assessed through the analysis of a target gas every 6 hours. The target gas is a cylinder of gas with accurately assigned concentrations of the target species determined at a central calibration laboratory (in this instance MPI-Jena). This target gas will be introduced to the system as a sample and following analysis the deviation of N2O and SF6 concentrations from the assigned concentrations will be calculated. We also take part in International inter-comparison programs (i.e. WMO round-robins, Cucumbers), see links.