The total measurement error of an analyser, including the
                           cross-sensitivity to other gases (see section
                              8 of appendix 4 of this Code), shall not exceed ± 5%
                           of the reading or ± 3.5% of full scale, whichever is smaller.
                           For concentrations of less than 100 ppm, the measurement error shall
                           not exceed ± 4 ppm.