Associated Press planned to change its broadcast feed speed early in 1970.
In preparation they sent out a "Do-It-Yourself" illustrated instruction book to all their radio and TV station customers. It was either that, or hire 3,000 technicians to make the change on the scheduled day!
https://www.navy-radio.com/manuals/tty/m15-AP-gearchange-1969.pdf
Cheers,
Nick England K4NYW
www.navy-radio.com