The Backing Boards are the two sheets of matboard that are placed on the CMC behind the sheet of matboard being cut.
Backing Board
Place Two Sheets of matboard on the CMC behind the sheet of matboard being cut to serve as Backing Boards. Full Definition
Troubleshooting:
Q: My cuts keep getting weird random jerky cuts along the edges.
The Backing Boards will need to be replaced if you see a lot of blade scoring into it to prevent the cutting blade from following along previous cuts cut into in the Backing Board.