A method for testing optical fibers, comprising: cleaving the optical fiber to produce a cleaved end surface; measuring, by measuring an optical signal emerging from the cleaved end surface using an optical testing instrument, values of a characteristic of an optical fiber, having a fiber axis, at a plurality of angles of rotation of the optical fiber generally around the fiber axis to generate from the measurements a plurality of data points indicative of measured values of the characteristic as a function of angle of rotation; characterised in that the method further comprises: creating a model of the optical fiber having the characteristic as a first variable parameter, having as a second variable parameter an instrumental quantity relating to the testing instrument, the instrumental quantity comprising a value of an angular alignment between the fiber and the instrument, and having as a third variable parameter a value of an angle between the cleaved end surface and the fiber axis; generating from the model a functional relationship between an expected measured value of the characteristic and the angle of rotation, the first variable parameter, the second parameter, and the third parameter; varying the first, second and third parameters to fit the functional relationship to the data points according to one or more predetermined criteria; and determining the value of the characteristic, the value of the angular alignment between the fiber and the instrument, and the angle between the cleaved end surface and the fiber axis based on the fit. cleaving the optical fiber to produce a cleaved end surface; measuring, by measuring an optical signal emerging from the cleaved end surface using an optical testing instrument, values of a characteristic of an optical fiber, having a fiber axis, at a plurality of angles of rotation of the optical fiber generally around the fiber axis to generate from the measurements a plurality of data points indicative of measured values of the characteristic as a function of angle of rotation; characterised in that the method further comprises: creating a model of the optical fiber having the characteristic as a first variable parameter, having as a second variable parameter an instrumental quantity relating to the testing instrument, the instrumental quantity comprising a value of an angular alignment between the fiber and the instrument, and having as a third variable parameter a value of an angle between the cleaved end surface and the fiber axis; generating from the model a functional relationship between an expected measured value of the characteristic and the angle of rotation, the first variable parameter, the second parameter, and the third parameter; varying the first, second and third parameters to fit the functional relationship to the data points according to one or more predetermined criteria; and determining the value of the characteristic, the value of the angular alignment between the fiber and the instrument, and the angle between the cleaved end surface and the fiber axis based on the fit. creating a model of the optical fiber having the characteristic as a first variable parameter, having as a second variable parameter an instrumental quantity relating to the testing instrument, the instrumental quantity comprising a value of an angular alignment between the fiber and the instrument, and having as a third variable parameter a value of an angle between the cleaved end surface and the fiber axis; generating from the model a functional relationship between an expected measured value of the characteristic and the angle of rotation, the first variable parameter, the second parameter, and the third parameter; varying the first, second and third parameters to fit the functional relationship to the data points according to one or more predetermined criteria; and determining the value of the characteristic, the value of the angular alignment between the fiber and the instrument, and the angle between the cleaved end surface and the fiber axis based on the fit.