Abstract: A load measuring sensor set on an aircraft is used under the control of a control unit on the aircraft. The load measuring sensor set is calibrated and there is calibration data associated with it. A code is retrieved which identifies uniquely the sensor set, so that a remote database can be interrogated using the code to retrieve the correct calibration data for the sensor set, for use by the control unit. The sensor set may utilise an optical-fibre having a Fibre Bragg Grating arrangement which provides optical signature characteristics that provide the unique code and having a Fibre Bragg Grating arrangement configured to measure loads.