Historical note: Up until the time of the Chalk Farm '84 ruleset, fare zones were orthogonal to the four quadrants, but by the time the Holland Park 2000 ruleset was released the growing size of the underground network had made the introduction of a fifth quadrant necessary. This means that post-Holland Park 2000, quadrant five now approximately coincides with fare zone one, while quadrants 1–4 have mostly been reinstated to their initial configurations. During much of the 16-year interim period between these two rulesets, quadrant five was an asymmetrical addition largely coinciding with the then-foetal Docklands Light Railway and Jubilee Line Extensions, and rulesets during this period often encountered a variety of curious side-effects. It is no coincidence that the helical stresses routinely encountered during this time forced far more rigorous study of spin, and this enhanced the understanding of many areas of the game.
Scholars and mathematicians are still evaluating the effects of the overlap between zone one and quadrant five, but it has obvious implications for the ongoing studies on advanced pickerings and for the gradual revival of the ratache and the glide.