Very interesting item. My eyes aren't very sharp anymore but the markings may be French or Russian. My opinion is that this instrument was possibly used on a Maxim machine gun and was possibly issued as part of the gunner's kit. The 1904 date stamp would indicate a very early issue, perhaps for Russian military use. Also, there appears to be an "arrow" marking that could either signify the direction of fire when setting the elevation, or it could also be an arsenal marking or logo. I can't make out the "crown" marking indicated by one of the posters but it also may be another arsenal or manufacturer's mark.
I enjoyed seeing this tool and it certainly is a nice addition to any collection.