Method for calibrating an irradiation device of an apparatus for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam (6, 10), which irradiation device comprises at least two irradiation units (3, 4), wherein a first irradiation unit is adapted to generate at least one first energy beam and guide the first energy beam via a first beam guiding unit in a first guiding region of a build plane, wherein a second irradiation unit is adapted to generate at least one second energy beam and guide the second energy beam via a second beam guiding unit in a second guiding region of a build plane, comprising the steps: - guiding one of the at least two energy beams (6, 10) via the corresponding irradiation unit (3, 4) to a determination region, preferably a part of a build plane, for generating a calibration pattern (18, 19) - imaging at least one part of the determination region to an on-axis determination unit (12, 14) of the at least one other irradiation unit (3, 4) - determining a position of the calibration pattern (18, 19) in the determination region on basis of the image of the at least one part of the determination region - generating calibration information relating to a calibration status of at least one part of the irradiation device based on the position of the calibration pattern (18, 19), - generating a first calibration pattern via the first energy beam guided via the first beam guiding unit to at least one first position in the build plane and determining at least one first parameter of the first calibration pattern in the at least one first position via the first determination unit assigned to the first beam guiding unit, and generating a second calibration pattern via the second energy beam guided via the second beam guiding unit to at least one second position in the build plane, characterized by determining at least one second parameter of the second calibration pattern in the at least one second position via the first determination unit. - guiding one of the at least two energy beams (6, 10) via the corresponding irradiation unit (3, 4) to a determination region, preferably a part of a build plane, for generating a calibration pattern (18, 19) - imaging at least one part of the determination region to an on-axis determination unit (12, 14) of the at least one other irradiation unit (3, 4) - determining a position of the calibration pattern (18, 19) in the determination region on basis of the image of the at least one part of the determination region - generating calibration information relating to a calibration status of at least one part of the irradiation device based on the position of the calibration pattern (18, 19), - generating a first calibration pattern via the first energy beam guided via the first beam guiding unit to at least one first position in the build plane and determining at least one first parameter of the first calibration pattern in the at least one first position via the first determination unit assigned to the first beam guiding unit, and generating a second calibration pattern via the second energy beam guided via the second beam guiding unit to at least one second position in the build plane, characterized by determining at least one second parameter of the second calibration pattern in the at least one second position via the first determination unit.