A mine is a complex underground structure. With its many tunnels and different levels, it can look like a labyrinth at first glance. But extraction was by no means carried out at random. Precise underground surveying was the basis for successful and safe mining.

The miners had to follow the valuable ore veins and rock layers as closely as possible. The hewer played an important role in this: thanks to his experience, he could distinguish valuable ore from ordinary rock. However, the direction of advance was determined by the mine surveyor. He surveyed the mine, entered new passages into the mine plans and thus, in a sense, created a floor plan of the mine underground.

The mine surveyor’s tasks were similar to those of a modern surveying engineer. He determined the boundaries of the mining claims above and below ground and ensured that the work did not break into neighbouring mines or encroach on someone else’s property. As early as the Middle Ages, mine surveyors were sworn officials. Their surveys had legal validity and were regarded as binding documents.

For their work, they used various measuring instruments, including a compass, protractor, measuring chain, measuring rope and an inclinometer.

They used the inclinometer to determine the angle of ascent or descent of a tunnel. This allowed them to specify how steeply a new mine working should rise or fall.

To determine the cardinal direction, they used a special mine compass known as a circumferentor. It was attached to a tightly stretched rope and indicated the direction of magnetic north. Because iron would have affected the compass, both the surveying instruments and the miners’ lamps were made with as few iron components as possible.

To ensure that the hewer drove the tunnel forward exactly in the specified direction, a so-called Teilung was finally lowered from the ceiling. It consisted of three cords weighted with stone weights, which were aligned precisely with a marking on the rock face. This simple but effective orientation aid helped the miners drive the tunnel forward centimetre by centimetre in the planned direction.