It is common knowledge that the blood pressure data detected in the same patient at constant intervals, after the artefacts rejection, are dependent and strictly correlated. Such a dependence is as much stronger as closer BP values are. For this reason we used the Fourier analysis, curtailed to the third term, based on time series. We obtained, in previous studies, a good fit between experimental data and the statistical model. We analysed a large normal population as control selected from a multicenter Italian epidemiologic study. In addition we take into account a wide group of hypertensives subdivided in accordance with the target organ damage. The Fourier model evidenced that it is likely to have a connection between the different factors involved in the regulatory mechanisms of blood pressure control and the first term syncronized on a 24 hour basis, i.e. able to fluctuate once a day, the second one twice, the last one three times, every eight hours, daily. The analysis allows a detailed evaluation of the blood pressure nocturnal fall and the incidental presence of a relative minimum in the early afternoon. We can also have the opportunity to evaluate the blood pressure peaks during late morning and late afternoon. The further step was to determine for each model, the tangents to the inflection points.