Once the end of your piece of wood is square, set the position of the cutter to mark out where you want the shoulder of your joint to be.   This would be suitable for mortise and tenon or half lap joints. 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. This is the ideal tool for marking out this joint. Repeat this for all similar joints.

If you are doing a tenon, position your cutter to cut 2 lines from either side of the wood to give you the correct size tongue of your tenon. eg: if your wood is 24 mm thick and the tongue of the tenon needs to be 10 mm thick, set up the cutter at 7 mm and mark both sides. 7+7+10=24

Note: For this to work the thickness of the rails must be consistent.  If not you will need to mark the joint out from one side by repositioning the cutter for the second cut.

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.

To mark out the mortise, cut the short lines for the bottom of the joint first, this is the width of the rail, then the top short line for the position of the haunch in the tenon. Thirdly, cut a line for the outside of the joint. From the same side as the third cut, cut the fourth line.

Note:   The large 100mm wide head gives this tool lots of controllability when you are required to cut parallel lines toward the maximum extension of the cutter.  Making this tool far superior to others with a small surface area on the head of the gauge.

The other nice feature of this gauge is the fact that the arm extends slightly past the cutter allowing you to hold the arm outside the cutter if required to cut a parallel line at the maximum extension of the gauge, very difficult to do when the cutter is right on the end of the arm like many other gauges.