The application allows measuring the horizontal and vertical distance of an electric cable by a system that is mounted on rails. The work takes place outside. A surface-measuring device is mounted in a box, the cover of which can be shifted to position the sensor. A drylin® N guide from igus® is used, which allows sliding on two axles. This system is subject to humidity and it needs to be dust- and dirt-resistant. dylin® N low profile guide systems reliably fulfil these requirements. Mounting is easy and the system is maintenance-free.