Hi,
Thank you for your comment!
The map source of the elevation of 1706 m is the 1:250K topographic map from the Surveyor General in Windhoek, 2214 Walvisbay (1982), as well as topographic map 1:50K 2215BB (see also https://namibia-topo.openstreetmap.org.za/)
These might not be the latest editions.

I also would like to refer to ALOS 
 World 3D dataset which includes a highest contour line at 1700m for this mountain.
And then to PeakVisor which does not only use SRTM for elevation model but also ASTER GDEM, the elevation of the mountain there is even higher.
(https://peakvisor.com/hiking-map?peak=sargdeckel#13.52/-22.02199/15.93181)

May I ask which topographic maps give the elevation with 1685m?
Best Regards





