Conversion gain averaged across all pixels of a flight H2RG Euclid detector measured at different integrated signals using linear, NL2, and NL3 mean-variance methods. For each method, a linear regression and its 1-sigma confidence interval are plotted. Only the NL3 mean-variance method is consistent with the hypothesis that the gain remains constant with integrated signal. The mean gain measurement is 2.5% lower when measured with the NL3 mean-variance method compared to the linear method.