Abstract: A method has been developed to calibrate the relative radiation response of sensors in an array by substitutional analysis of the sensor outputs caused by a radiation field wider than the array. The array is positioned in the wide field in such a way that the sensor positions in the array are exchanged once by translation in order to calculate ratios of neighboring detector sensitivity and once by rotation in order to calculate ratios of mirror detector sensitivities. There is no dependence on dose reproducibility, field flatness or symmetry. The method requires that the profile shape produced by the machine during each measurement be reproducible and that the array movements do not affect the scattering conditions.