Not mine, but found on the web today: Siemens & Halske Wahlimpulszeitmesser. Literally a dial-pulse-time-gauge ;) all put together in one of the infamous German compound nouns. The techs also found it awkward and just called it a WIZM.
It's a tube oscilloscope with extra long afterglow. I suppose it acts much like a modern soundcard oscilloscope, audio analyzer or this software (http://www.classicrotaryphones.com/forum/index.php?topic=21454.msg218706#msg218706).
I never knew it existed and thought I might present it here. The first pic is from the Aachen telephone museum (http://www.fernmeldemuseum-aachen.de/html/entstoer.html) which has one on display:
(http://www.fernmeldemuseum-aachen.de/pict/entstoer_totale.jpg)