One of the principles of SuperMemo is to formulate simple and univocal items. However, even the simplest item may be quite hard to remember. Numbers are a notorious example of intractable polluters of SuperMemo databases. The problem with numbers is that they are all similar to each other and can easily be confused. Here, the help comes from techniques which are as old as the art of learning itself, the mnemonic techniques.
Any good mathematician may demonstrate that remembering numbers is much less of a problem
to him than to an average man in the street. Having had to learn hundreds of constants and formulas, a mathematician more or less consciously knows how to deal with them. The simplest technique is the learn a list of 10, 20 or 100 pictures associated with numbers. For example: 1 - harpoon, 2 - coin, 3 - tripod, 4 - dog, 5 - hand, etc. Knowing such associations, numbers may easily be represented as colorful pictures. For example: 4315 may be seen as a dog on a tripod harpooning somebody's hand.
Despite what may seem at first, time spent on forming the pictures is incomparable with gains produced by successful memorization. By virtue of the brain circuitry developed in the course of evolution, vivid pictures are by far easier to remember than dry numbers.
In SuperMemo, it is always better to invest heavily in formulation of items, in order to have only a couple of repetitions in the lifetime.
Ill-structured or intractable items may be repeated as many as 30 times in the course of a single year!!!