I have found an Ottoman/Turkish direct fire sight with the Arabic-Indic numbers "8,7cm" at the top and a maximum range of 4,200 meters indicated in Arabic-Indic. The sight post will fit the German 9cm C/1873 and the Prussian export version of the 8cm C/1864. The maximum range is a bit short for the 9cm C/73 and even though the range makes sense for the 8cm C/64 the "8,7cm" marking seems to preclude this possibility. Any ideas about what this sight could be for?