Anyone involved in the markets, on any time scale, will verify the fundamental need for Technical Analysis in making trading/investment decisions.
Many publications diversify into (very) esoteric theories about T.A., which may or may not be profitable, according to the individuals application.
I have found this book to be clear and concise, explaining the underlying concepts of T.A. in a way that anyone approaching the markets, cash in hand, needs to read to be "grounded" and enabling the reader to further study any given method of choice.
The term "Bible" has been used for this book, I would say for myself, that along with Nison's "Japanese Candlestick Charting Techniques" and Bulkowski's "Encyclopedia of Chart Patterns" this book is a constant reference source which needs re-reading and keeping on the desk.