Sometimes, it seems like a vortex is simply never going to grow, and that you are just pouring mana down a large drain, never to be seen again. With this skill, you can finally know for sure!
The trick is in recognizing the various little eddies and currents that are flowing within the pool of magic. In truth, anyone with the proper training can do this for any vortex, whether they are magically bound to it or not.