For many years, the water levels of the Havel were measured by the Brandenburg main gauge, which is located on Mühlendamm opposite Heidrichs-Mühle. The tower-shaped, functional building made of red bricks was built in 1904 in the headwaters of the Havel. In order to be able to measure the water level of the Unterhavel at the same time, the level house was connected to the underwater. The so-called inlet led under the Mühlendamm and directed the water of the lower Havel to the level shaft. Here it then rose due to the effect of communicating tubes.
The Havel level is still measured here. Not far away are the former water mills of the Neustadt, which have been using the level difference to drive their mills since the beginning of the 13th century by damming the Havel by 1.20 m.