At first glance, the situation seems hopeless. For a long time researchers have acted so-called trial and error. This means that the structure and come up with a look at whether or not it is combined with the experience. But it does not go far. They were invented ways to circumvent this difficulty. A crucial role is played by electronic computers. I would like to give the reader an idea of ??how this problem is bypassed, but our conversation about the X-ray analysis was delayed. "Tricks of the Trade" resorted to the researchers, it is, first, an introduction to the structure of a heavy atom (then can be considered as a first approximation, that the crystal consists of one of these atoms) and, secondly, a very elegant theory, which shows between different structural amplitudes are due.