The finished joint

Mark the slope of the wedge on the side of the tenon with its back up against the marked line. Carry the line around the tenon with a try square. Use the mortise marking gauge to mark the thickness of the wedge on the tenon.

Pare out the mortise with a chisel, again working from both sides. Be careful to follow the marked line on the tenon side in order to get the correct angle for the wedge. Assemble the parts and drive the wedge in to pull the joint up tight.

The finished joint should look something like this.