Measuring system for equipping or retrofitting a device for manufacturing a three-dimensional object by selective layerwise solidification of a building material , wherein the device includes an irradiator for selectively irradiating a layer of the building material applied in a working plane of the device at locations corresponding to a cross-section of the object to be manufactured, for solidifying the irradiated locations, the irradiator comprises at least two irradiation units , preferably laser arrays, and each irradiation unit can be imaged onto a pixel in the working plane and is at least switchable on and off, said measuring system includes: - at least one camera for determining and evaluating the radiation emitted by the irradiator and/or the position and/or orientation of the irradiation unit(s) in absolute and/or relative to one another, - at least one distance sensor for detecting an extension in a direction (z) perpendicular to the working plane , - a power measuring device for determining a radiation power of the irradiator and/or of at least one of the irradiation units , and - a measuring head holder , wherein the measuring system is configured such that the camera , the distance sensor and the power measuring device are mounted in a fixed position relative to each other on the measuring head holder and are arranged in the device in such a way that the camera can acquire an optical image of the irradiator from below and such that the distance sensor can determine the vertical distance in the z-direction to an element located above the sensor, wherein the at least one camera and the at least one distance sensor are preferably integrated in a single measuring device. the device includes an irradiator for selectively irradiating a layer of the building material applied in a working plane of the device at locations corresponding to a cross-section of the object to be manufactured, for solidifying the irradiated locations, the irradiator comprises at least two irradiation units , preferably laser arrays, and each irradiation unit can be imaged onto a pixel in the working plane and is at least switchable on and off, said measuring system includes: - at least one camera for determining and evaluating the radiation emitted by the irradiator and/or the position and/or orientation of the irradiation unit(s) in absolute and/or relative to one another, - at least one distance sensor for detecting an extension in a direction (z) perpendicular to the working plane , - a power measuring device for determining a radiation power of the irradiator and/or of at least one of the irradiation units , and - a measuring head holder , - at least one camera for determining and evaluating the radiation emitted by the irradiator and/or the position and/or orientation of the irradiation unit(s) in absolute and/or relative to one another, - at least one distance sensor for detecting an extension in a direction (z) perpendicular to the working plane , - a power measuring device for determining a radiation power of the irradiator and/or of at least one of the irradiation units , and - a measuring head holder , wherein the measuring system is configured such that the camera , the distance sensor and the power measuring device are mounted in a fixed position relative to each other on the measuring head holder and are arranged in the device in such a way that the camera can acquire an optical image of the irradiator from below and such that the distance sensor can determine the vertical distance in the z-direction to an element located above the sensor, wherein the at least one camera and the at least one distance sensor are preferably integrated in a single measuring device. <EOS>