If you are experimenting, you must remember that Mach 3 must run into cutter compensation, In other words, it is no good lining up your work, then switching on cutter compensation and expecting Mach 3 to jump to one side or the other to apply the compensation.
If you are cutting, say, a circle in a plate, then start at the circumference of the circle (without cutter comp). Your first move should be to apply cutter comp - G41 or G42. The second move is move round the circumference of the circle a short distance - say a quarter turn G2 or G3. This is the move that Mach uses to apply the compensation. The third move should be then to cut the circle, drop z, then - G2 or G3 Bear in mind that the tool table must have the cutter diameter, and the correct tool must be selected.
G41 and G42 depends on whether you are using G2 or G3 (which direction your tool is travelling) and whether your tool is inside or outside the circle.
Try replacing your cutter with a felt tip pen, and drawing it out on a sheet of paper, you will be able to see the different paths, particularly if you try doing the circle first, then using compensation. The way Graham drew it, I am quite sure he has it in his head as a fixture, but to us lesser mortals, it could be a good reminder to then pin the diagram on the workshop wall.