The author starts by ripping a sheet of 7/16-inch OSB into 5 1/2-inch widths.
He sets the fence to 1/2 inch (left) and adjusts the height of the saw blade to 2 13/16 inches (right).
Next, he sets the bevel of the table saw to 3 degrees. It is important that the blade is tilting toward the fence. If everything is set correctly, the table saw should look like this
He runs one side of the ripped OSB through the saw ...
Then he flips the board over and runs it through the saw again.
The completed backer board has a recess a little over 1/4 inch deep.
With the backer board positioned between framing members, the butt end of a sheet of drywall will be pulled in slightly when both panels of the butt joint are secured.
The slight recess is the perfect amount to speed up finishing of butt joints.