Learning Gann's theory is best to buy the original translation. Gann theory self-study can generally start with the following books:

Watch Forty-five Years of Wall Street. It's classic and easy to understand. At the same time, you can refer to Gann's "Stock Market Rules-Classic Translation of Stock Market Investment" for mutual reference.

Then there is Sixteen Lectures on Gann's Theory Analysis and Practical Application, which is a comprehensive and good book about Gann's theory at present.

Then, combined with the reality of China's securities and futures investment, this paper comprehensively and systematically introduces Gann's investment theory and skills.

Finally, there is a book, advanced space and market geometry of Gann's theory, which requires a certain mathematical foundation and is an advanced book for studying Hong En's theory.