Abstract: The ultimate aim of this study is to make detrended fluctuation analysis (DFA) useful for everyone. It introduces a practical method for making a device that can check cyclic rhythm in nature, such as the heartbeat. This book presents empirical evidence revealed by a modified DFA (mDFA). A heartbeat-checking algorithm, DFA, was made by Peng et al. in the mid-1990s. However, the technique has not been incorporated in a device for practical use. With a view to creating a device DFA, mDFA was made by modifying Peng's DFA and a former graduate student (Katsunori Tanaka) created the program under supervision of the author. To verify mDFA, hundreds of cyclic phenomena were studied and recorded.