A method and a device measure for a deformation of a fuel element of a pressurized water reactor having a plurality of control rod guide tubes. A probe displaceable in the direction of the longitudinal axis of the control rod guide tube is inserted in the interior of at least one control rod guide tube having at least one reference axis, and supported in at least one section of the control rod guide tube on the interior wall thereof, such that the orientation of the at least one reference axis is unambiguously a function of the orientation of the longitudinal axis of the control rod guide tube in the section. The orientation of the at least one reference axis in the section of the control rod guide tube is determined relative to the orientation of the or a further reference axis of the probe in a different section.