Construction device and method for determining the position of a drill drive

The apparatus (10) has a support device and a mast (20). The mast is movably mounted on carriage (30) to which a rotary drive (32) for rotatably driving a drilling tool (36) is arranged. A measuring device (40) is provided for determining the position of a measuring point defined in the mast head (26). A measuring device (50) is provided to determine a positional deviation in the horizontal direction between the position of measuring point at mast head and the carriage arranged in the drill drive. An independent claim is included for a method for determining the position of the drill drive.