In the Epitome Location there are different effects, which are all based on the same principle. They are based on the principle that if you count all the pips of a full deck together, you arrive at 364 (jokers not included). If someone selects a card and keeps it aside, you can find out which one it is by counting the pips of the remaining cards and subtacting it from 364. Harry Lorayne simplified the calculations so that he is able to make them faster and more practical for in the real world.
Remco De Wolf