Hello again, I am having this problem understanding Quantum Theory, when it comes to calculations and applications. I'll give you an example. When using the Bohr Sommerfeld quantization rule we use calculus in...what? Is it an oscillating particle?? That's what I can't seem to understand. Or (this is from some solved exercises I was working on before) when using the WKBJ semiclassical approximation, after putting momentum under the integral, I noticed that the solution had a number multiplying the integral, either 2 or 4 (sometimes there wasn't any). So I have concluded that the WKBJ integral is multiplied by the number of times we want that specific part of the full oscillation of the particle we are studying. Is that really it? I hope you can understand what I am talking about! I also think that it all has to do about the potential Energy U(x), or even something about a potential well. I really need some guidance over the matter. I would really appreciate it if you could guide me!