A calibration ledge serves for calibrating a manufacturing device for manufacturing a three-dimensional object 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. The calibration ledge has an elongated shape and includes 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.