Considering the Atlas experiment, which are the basic theoretical decisions someone must take in order to create an effective calorimeter? In other words, which are the basic problems that someone must solve to achieve the best possible effectiveness? For example, the high temperature problem can be solved with cryogenic methods (Liquid Argon). The geometrical orbits of particles can be fully observed if we construct our calorimeter in the shape of a barel. Are there any similar problem that physicists had to face?