A calibration device for calibrating a manufacturing device for manufacturing a three-dimensional object within a build area by a layer-by-layer solidification of a building material at the points corresponding to the respective cross-section of the object by selectively irradiating layers of the building material with a radiation in a working plane, wherein the manufacturing device comprises an irradiation device capable of selectively directing a radiation suitable for solidifying the building material, preferably laser radiation, radiation of a gas laser being further preferred, to different points of the working plane within the build area, wherein the calibration device comprises: a calibration ledge having an elongated shape, wherein the calibration ledge comprises an aperture ledge extending in its longitudinal direction and comprising several aperture openings arranged in a row in the longitudinal direction of the calibration ledge which are more permeable for the radiation of the irradiation device than the region of the aperture ledge surrounding the aperture openings, the calibration ledge further comprises a sensor ledge extending in its longitudinal direction, arranged substantially parallel to the aperture ledge, and comprising at least one surface sensor capable of detecting the radiation of the irradiation device, and the calibration ledge is mountable in the manufacturing device such that the radiation of the irradiation device can hit the at least one surface sensor through the aperture openings, wherein the calibration ledge is preferably mountable in the manufacturing device such that the aperture ledge lies in the working plane of the manufacturing device, and wherein the calibration device further comprises at least one evaluation unit suitable for evaluating an output signal (s(t)) of the at least one surface sensor, wherein the at least one evaluation unit is suitable for determining for one aperture opening amplitudes A and/or lengths L of single pulses P contained in the output signal, setting up a spatial distribution of the determined amplitudes and/or lengths, and evaluating this spatial distribution, wherein a single pulse P is a pulse in the output signal (s(t)) of the surface sensor that is generated by scanning the aperture opening by a radiation of constant intensity. a calibration ledge having an elongated shape, wherein the calibration ledge comprises an aperture ledge extending in its longitudinal direction and comprising several aperture openings arranged in a row in the longitudinal direction of the calibration ledge which are more permeable for the radiation of the irradiation device than the region of the aperture ledge surrounding the aperture openings, the calibration ledge further comprises a sensor ledge extending in its longitudinal direction, arranged substantially parallel to the aperture ledge, and comprising at least one surface sensor capable of detecting the radiation of the irradiation device, and the calibration ledge is mountable in the manufacturing device such that the radiation of the irradiation device can hit the at least one surface sensor through the aperture openings, wherein the calibration ledge is preferably mountable in the manufacturing device such that the aperture ledge lies in the working plane of the manufacturing device, and wherein the calibration device further comprises at least one evaluation unit suitable for evaluating an output signal (s(t)) of the at least one surface sensor, wherein the at least one evaluation unit is suitable for determining for one aperture opening amplitudes A and/or lengths L of single pulses P contained in the output signal, setting up a spatial distribution of the determined amplitudes and/or lengths, and evaluating this spatial distribution, wherein a single pulse P is a pulse in the output signal (s(t)) of the surface sensor that is generated by scanning the aperture opening by a radiation of constant intensity.