The mobile measuring case enables a fast and cost-effective automated absolute initial measurement for plant extensions or commissioning. Only the tolerance field in which the tool may move and the starting position of the measurement must be defined beforehand. The tool is then moved once to the center of the light barrier and tool data is generated. The robot then moves the tool within the defined tolerance field and measures itself automatically using the supplied programs. The advantages are the high accuracy and the automated, standardized and reproducible sequence.