A retractable assembly for immersion-, flow- or add-on measuring systems in analytical process technology for measuring at least one measured variable of a medium in a containment, comprising: an essentially cylindrical housing; an immersion tube, which is movable axially in the housing between a service position out of the medium and a process position in the medium; and a sensor for measuring the measured variable. The sensor is arranged in the immersion tube, wherein the sensor protrudes at least sectionally out of the immersion tube at the end of the immersion tube remote from the medium; and an openable and closable cover, which surrounds at least the section of the sensor protruding out of the immersion tube. The sensor in the opened state of the cover is mountable and demountable, respectively, in and from the immersion tube. The retractable assembly is characterized in that the cover at least sectionally travels with the movement of the immersion tube and in the process position is located at least sectionally in the housing.