INTRODUCTIONSince Riva-Rocci invented indirect brachial cuff sphygmomanometry in 1896 1 and Korotkoff proposed the auscultatory method in 1905, 2 the method for blood pressure (BP) measurements has remained essentially unchanged for the past 100 years.In 1969, Posey et al. 3 identified mean BP on the basis of the cuff-oscillometric method. With subsequent theoretical and technical improvements, the method to determine systolic and diastolic BP (S and D, respectively) was introduced to the cuff-oscillometric method. As a result, many of the automatic electronic sphygmomanometers available today have adopted this method, and those different from the auscultatory method have begun to be used in general clinical practice. Since the advent of indirect methods for sphygmomanometry, the past century has developed the practical and clinical sciences of hypertension. However, BP information necessary for the diagnosis and treatment of hypertension is still obtained essentially on the basis of casual measurements at the outpatient clinic (clinic BP). However, the reliability of clinic BP was called into question 40 years after the advent of indirect sphygmomanometry. In 1940, Ayman and Goldshine 4 widely adopted the concept of self-BP measurements in the field of clinic BP measurements and demonstrated discrepancies between clinic BP and self-BP measurements. Bevan, 5 in the United Kingdom, first reported the results of ambulatory BP (ABP) monitoring (ABPM) using a direct arterial BP measurement method in 1969, and showed that human BP changes markedly with time. The quantity and quality of BP information vary greatly according to different methods, and the problem of interpreting clinic BP, which is obtained specifically in a medical environment, has been an issue in the clinical practice of hypertension during the past 50 years.However, the practice and epidemiology of hypertension still depend entirely on BP information obtained in a medical environment (clinic BP/BP at a health examination), resulting in the