This is a Flugzeug-Höhenschreiber or Barograph numbered 2651 and manufactured by Emil Scholz of Hamburg with an inspection stamp still attached by wire and marked 1918 and with its original, fabric-wrapped  rubber 'bungee' shock cords.  The internal mechanism would be set and then slid into its wooden box, locked and attached to the wings of an aircraft.  Just before climbing into his cockpit, the pilot would flip a switch on the outside of the box starting it's recording drum to slowly turn.  As the pilot gained altitude, the pen on the drum would rise and record his altitude.  Once the pilot returned to his aerodrome, the paper roll could be read to determine how high he had flown.  In one contemporary photo, a flight instructor is seen reading the recording paper and, in another, the instrument is seen suspended from the upper wing of an A.E.G. bomber in flight.  Our Höhenschreiber is seen in a drawing from the book Flugzeuginstrumente by Dr. Kurt Bennewitz, Berlin, 1922, with the same shock cords making this example extraordinarily rare.