Abstract: A method for establishing the genotype of the locus is provided in which a series of calibration samples are analysed, the results being one of three indication types, a window being defined relative to the indication for each of the indication types, unknown samples being similarly analysed with the window that they fall within being taken to determine the indication type for the unknown sample and hence the genotype of the relevant locus. The technique provides a robust, reliable and accurate method of genotyping which is suited to automation.