Wild ZNL 16 Zenith and Nadir Plummet. Used for vertical plumbing over longer distances.
Being detachable from the tribrach the ZNL (which has a plumbing accuracy of 1/30 000) can be centred over or under the required point and then replaced by the theodolite with guaranteed forced-centring. For some tasks, particularly those connected with large constructions, the ZNL can be used as an independent instrument. For engineers it is particularly useful when working on towers.