Abstract: A topographic bench mark unit comprises a case which defines internally a space accessible through a movable lid. The case is mounted on a support. A bench mark member is integral with the case within the space. Provision is made for mounting a topographic member in a predetermined position in relation to the bench mark point, with a view to producing measurements referring to this point, and means for identifying the bench mark point. The unit has application both to immovable altimetric and geodetic bench marks.