Once the end of your piece of wood is square, set the position of fixed cutter to mark out where you want the shoulder of your joint to be. The moveable cutter is held in the head of the gauge during this process. This would be suitable for mortise and tenon or half lap joints and is basically used as a cutting gauge for this part of the marking out.  Repeat this for all similar joints.

Note: This cut line leaves  a 90 degree edge so you can  plane just to the cut line giving  you the perfect crisp shoulder to form a great looking joint.

If you are doing half lap joints, position your cutter to cut a line in the centre of the wood. Repeat this for all similar joints.

For marking out mortise and tenons this tool is the most accurate and efficient. Using the screw adjustment position the two cutters so they are the width of the desired tenon apart as shown in the adjacent photo. Then move the head of the gauge so the two parallel cutters end up in the desired position, usually in the middle of the rail.

Note: For fine adjustment of this gauge, semi tighten the knob when the gauge head is close to the desired position but so that the head has to be moved slightly toward the cutter by squeezing your thumb and index finger up against the back of the head as shown in the adjacent photo.   You will find this method allows you to move the head slowly and accurately into position.  Once in position tighten the knob.

Once you have set the cutter in  position the gauge can then be used to mark out the tongue of the tenon very accurately as shown in the photo.

To mark out the mortise, position the two cutters to mark out the two short lines for the top and bottom of the joint as shown in adjacent photo.

Lastly position the cutter to mark out the width of the mortise to suit the tenon.

You are now ready to cut out your mortise and tenon joints using your desired method.