Great article. One nit though. When making a 2d Cartesian graph with the two axis there are accepted quadrant labeling practices [1]. Quadrant I is positive on both axis, Quadrants II and IV positive on just one axis, and Quadrant III is negative on both. What you described as Quadrant IV should really have been Quadrant III. You can flip axis any which way, but the opposite quadrants will always have 1 step in between them. No big deal, but will make little sense if somebody actually tries to visualize your model.