Ingenious use of hand shapes to recall the structure of formulas in Electrodynamics. The kernal of this wisdom is that the hand is one of the few “devices” that must be allowed in any testing situation for students. Yes, I know there is an iPhone app for each formula that plots in 3D, etc. But what if you had solve these equations after a ship wreck?
Interestingly, by duality you can prove that the better and more “organized” your books look to the eye; the more impossible they will be to find. At least for other people. The fact that people remember their own books by color of exterior may actually help you find a color coded bookshelf arrangement.