NavList:

Bill is right, of course, it is a Plath artificial horizon SOLD sextant, the artificial horizon provided by a gyroscope as opposed to the bubble in the other type of SOLD. SKS obviously can be spelled out as SOLD Kreisel Sextant. The National Maritime Museum holds quite a few - donated from different government agencies who took them off German planes and (U-)Boats after WWII. They are depicted and described in Willem Mörzer Bruyns wonderful "Sextants at Greenwich", p. 233 - 239.

What SOLD stands for still is unclear, unfortunately the Plath archives were destroyed when Hamburg was bombed during "Operation Gomorrha" in the summer of 1943. The literature on Plath does not give an explanation and persons that could have all died by now.

The instrument discussed here seems not to stem from the navy as the navy instruments were usually marked "M" (for: Marine).  As for the value: I recently acquired a bubble SOLD quite cheaply, it is in working condition thanks to Bill who repaired it but lacks the case and the telescope. Bill has written about it and another SOLD in his blog.

One last remark: the "Deutsche Seewarte" (bottom right of the instruction leaflet) was the German hydrographic institution until WWII, its successor was the Deutsches Hydrographisches Institut (DHI) now named Bundesamt für Seeschiffahrt und Hydrographie (BSH). The "Seewarte" tested sextants and chronometers and issued pilot books etc. It's got nothing to do with the coast guard as has been suggested here.

Regards

Wolfgang