This is a shell casing from the First World War. Found at an old home in Dubrovnik, Croatia, (Home of my friend's grand-dad's)
I am curious about the meaning of the different markings.
the shell was manufactured by
GR - Georg Roth AG. gun case factory, Vienna, III, Erdbergerlande 30 (The picture shows the base of a 7 cm 1899M pointed cannon shell casing with production and acceptance data from 1914)
a translation from www.arme-a-feu.wikibis.com says
Georg Roth AG bears the name of its founder. This cartridge factory was active from 1890 to around 1945. Its factories were located in Vienna (Austria) as well as Bratislava (the latter becoming independent in 1918).
Wikipedia has the following information regarding one of the mountain guns used to fire the shells
The 7 cm Gebirgsgeschütz M 99 was a mountain gun used by Austria-Hungary during World War I. It was obsolete upon introduction as it had a bronze barrel, a spring-loaded spade to absorb the recoil forces and it had to be relaid after every shot. The high elevations required of mountain guns greatly complicated the provision of barrel recoil systems as the breech could recoil into the ground, and it would be some years before satisfactory systems were developed. These would result in the 7 cm Gebirgsgeschütz M 8 and M 9 that used the same barrel and ammunition as the M 99, but had Gun shields and more advanced recoil systems. These guns weighed 402 kilograms (886 lb) and 456 kilograms (1,005 lb) respectively, although the exact differences between them are unclear other than they broke down into four and five loads for transport respectively.
The Gebirgsgeschütz M 99 broke down into three loads for transport
Most of the markings are already explained by @bookmanu, but "Wdf" seems to be an abbreviation for Wöllersdorf which is close to/in Vienna and was the location of a large ammunition factory.