Mark,

I also do not see how this selector works.
Peter Oberhammer opened his shop in Munich in 1872. Interesting to see that the company still exists:
http://www.waffenmuenchen.de/

In 1878 Oberhammer filed a German patent for selectors for drillings.
PeteM from this forum has found details:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=223652

However the selector in the patent drawing looks different (and very sketchy) and it's also hard to see how this one works.
The locking mechanism shown in the patent also looks "ancient", and is replaced by a more stable Jones underlever.

fuhrmann