1. A measurement method for use in an electron microscope equipped with a segmented detector having a detection surface that is divided into a plurality of detector segments, the method being adapted to measure the directions of the detector segments relative to at least one STEM (scanning transmission electron microscope) image, said measurement method comprising the steps of: defocusing the STEM image to thereby cause a deviation of the STEM image; and measuring the directions of the detector segments relative to the STEM image from the direction of the deviation of the STEM image.