During WW2 German field switchboard operators were required to use Message Forms (Spruchformularen) to record the times that calls were received or made.
I acquired a vintage Nachrichten Fibel (Signals Handbook) which included blank sample Spruch Formularen in the back for practice.
I removed one of the sample forms from the handbook and had my local print shop make a gummed tablet of the forms which I display and talk about at reenacting events.
To learn more about the forms, check out my book which is available through the Lulu Press Bookstore for $44.99 (US) plus shipping.