Here are links to videos detailing the operation of the Sound Devices 688 recorder and its companion CL-12 fader controller (aka "mixing board").
The first video is about the 688 recorder, and was made by sound mixer Blas Kisic for my CSUN advanced sound class. Blas is generously sharing this video with the whole sound and educational communities.
Basic operation of Sound Devices 688 recorder by Blas Kisic
The next series of 7 videos were produced by Sound Devices, and cover the detailed features and operation of the CL-12 fader controller. These videos can be found on Sound Devices' YouTube channel, but are free for non-commercial viewing.
Operation of the sound devices CL-12, videos by sound Devices
1: Touring the CL-12
https://www.youtube.com/watch?v=XBuIQBXkTAc&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=2&t=0s
Chapter 2: CL-12 Connection to the 688
https://www.youtube.com/watch?v=TZN04k6x3nc&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=2
Chapter 3: CL-12 Menus
https://www.youtube.com/watch?v=J8nHNhOB7ZU&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=3
Chapter 4 : CL-12 Channel Select Tools & PFL
https://www.youtube.com/watch?v=fkrJOdYR2_0&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=4
Chapter 5: CL-12 EQ & Outputs
https://www.youtube.com/watch?v=htCp9Bj6IDY&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=5
Chapter 6: CL-12 Metadata
https://www.youtube.com/watch?v=3WXAnioNWds&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=6
Chapter 7: CL-12 Shortcuts, COMs, and Remaining Buttons
https://www.youtube.com/watch?v=qb4CvdQxqIU&list=PLKpAunZPiGRnhbWuQRmkjNL331mCz6415&index=7