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.