The initial measurements with linear polarization technique on steel embedded in concrete show immediately that the controlling parameter of the corrosion rate value is the degree of saturation, as it controls the concrete resistivity. In present paper is given some old values and those found in specimens exposed to the atmosphere and rain during more than 25 years. The results show the importance of the degree of saturation, but also the fact that it is irregular in the cover depth as the rain penetrates by capillarity and takes some days to reach the bar surface with a cover depth of 3 cm. This fact of the gradient of humidity in the concrete surface is one of the reasons of the dispersion when the degree of saturation of the bulk resistivity is represented with respect to the corrosion rate. Also are commented the expression of the moisture content as volumetric fraction instead as water saturation degree. Average values and standard deviations are commented as well as some simplified equations for the calculation of the corrosion rate from the degree of saturation.