NavList:

http://collections.rmg.co.uk/collections/objects/43306.html

Thanks again Wolfgang.  One test of the nomenclature accuracy might be to do a Google search for the tern.  Your new formal term turns up very little.  The former, briefer term however found an earlier Zeiss version of the instrument in a British museum.  Looking at the provenance, I suspect the donor, who received it aboard a German ship, had taken notes including the German nomenclature name, or perhaps it is marked on the device.  The museum's description of it sounds quite certain regarding the name.