Pappenburg gauge and cryptic markings

[Dowly]

Originally Posted by Onkel Neal

http://www.wolfpackgame.com/img/research/pappen1.jpg

If I'd have to guess, the left one shows the depth in relation to the periscopes.

The right one seems to show the same for other parts of the boat. For example, on the right side there's a conning tower (brücke) mark at -9,7m. So, to get the boat submerged fully, the water level inside the tube would have to raise above that mark.

No idea what the markings on the left side mean.