Method for operating a manufacturing device for additive manufacturing of a three-dimensional object by application in layers and selective solidification of a powdered building material within a construction site lying in a working surface, the manufacturing device having at least two scanning units which are designed and arranged in order to in each case direct a beam of a relevant first or second beam source, which beam is controlled by the relevant first or second scanning unit, respectively, onto different target points on the construction site, a first sensor unit being assigned to at least the first scanning unit, the detection region of which sensor unit is directed onto the target point of the first scanning unit by the first scanning unit, the method comprising the steps of: directing the detection region of the first sensor unit onto at least a first portion of a test body region by means of the first scanning unit, without the first scanning unit directing a beam onto the test body region, irradiating at least part of the test body region with a beam that is directed onto the test body region by the second scanning unit, and in particular evaluating measurement signals detected by the first sensor unit, characterized in that the irradiation by means of the second scanning unit takes place following an irradiation process in which initially powdered building material was solidified, the irradiation with the beam of the second scanning unit takes place in a pulse-like manner and on the already solidified part of the building material in the test body region, the pulse-like irradiation is carried out in such a way, in particular with such an intensity, that the already solidified building material does not melt, and the detection region (30a, 30c) of the first sensor unit (26a, 26c) detects a solidified region of the building material that is spaced apart from the part irradiated in a pulse-like manner. the manufacturing device having at least two scanning units which are designed and arranged in order to in each case direct a beam of a relevant first or second beam source, which beam is controlled by the relevant first or second scanning unit, respectively, onto different target points on the construction site, a first sensor unit being assigned to at least the first scanning unit, the detection region of which sensor unit is directed onto the target point of the first scanning unit by the first scanning unit, the method comprising the steps of: directing the detection region of the first sensor unit onto at least a first portion of a test body region by means of the first scanning unit, without the first scanning unit directing a beam onto the test body region, irradiating at least part of the test body region with a beam that is directed onto the test body region by the second scanning unit, and in particular evaluating measurement signals detected by the first sensor unit, characterized in that the irradiation by means of the second scanning unit takes place following an irradiation process in which initially powdered building material was solidified, the irradiation with the beam of the second scanning unit takes place in a pulse-like manner and on the already solidified part of the building material in the test body region, the pulse-like irradiation is carried out in such a way, in particular with such an intensity, that the already solidified building material does not melt, and the detection region (30a, 30c) of the first sensor unit (26a, 26c) detects a solidified region of the building material that is spaced apart from the part irradiated in a pulse-like manner. directing the detection region of the first sensor unit onto at least a first portion of a test body region by means of the first scanning unit, without the first scanning unit directing a beam onto the test body region, irradiating at least part of the test body region with a beam that is directed onto the test body region by the second scanning unit, and in particular evaluating measurement signals detected by the first sensor unit, characterized in that the irradiation by means of the second scanning unit takes place following an irradiation process in which initially powdered building material was solidified, the irradiation with the beam of the second scanning unit takes place in a pulse-like manner and on the already solidified part of the building material in the test body region, the pulse-like irradiation is carried out in such a way, in particular with such an intensity, that the already solidified building material does not melt, and the detection region (30a, 30c) of the first sensor unit (26a, 26c) detects a solidified region of the building material that is spaced apart from the part irradiated in a pulse-like manner.