An instructor at a flight school has slid the metal recording mechanism out of the Flugzeug-Höhenschreiber or height recorder on the left and is reading a paper tape showing the height his pupil reached.  Manufactured by the company "Anton Ott, Kempten," this height recorder apparently has a small, 3-speed gearbox to change the number of revolutions, though I have not taken apart the recording drum to see this.  At the top of the metal plate with the handle is written Umdrehungszeit Std or Rotation Time and in the adjustable window is the number "2."  The compny logo and "No. 2984" and "DRGM" are written on the metal side under the pull-out handle.  Inside, the number "2198" is written in ink and pencil on the wood case.  A trademark of an "R" within a triangle (see below) is stamped into the wood and the numbers "4 18" suggesting that the wood case was manufactured in April of 1918.  The tradement looks exactly like the one used by the German propeller manufacturer, Reschke; perhaps they made the wooden box for Anton Ott.   You can see another instrument just like this one and made by this company at this link.