After having some bad luck with marks and leves, I ended up being level 24 before I could purchase Triangulate III, however I noticed that I could also purchase Triangulate IV now (instead of what I expected to be level 30). I checked around a few sites but all sites list Triangulate IV's (and everything elses) optimal rank(30) only, instead of it's purchasable rank. It's left me very curious if I should wait for Triangulate V.

Does anyone know at what ranks all the abilities become purchasable? Or a link to a site that does?