The Betriebsurh (station clock) was used at all WW2 German switchboard exchanges to record time that calls were received/sent. These clocks, actually chronometers, were hand-wound and were highly accurate. They were made by various manufacturers, including Junghans and Kienzle, according to Wehrmacht specifications.
Messages received and sent were recorded on special forms as shown below. These form included spaces for time read off of the switchboard’s Betriebsuhr.
Betriebsuhren are fairly common, but in most cases, very expensive, especially in working condition. Keep in mind that these clocks are repairable by any reputable clock/watch repair shop.
WW2 German Field Telephone Equipment 