Fig. 4. Calculated period P as a function of water content for (a) the six CS615 sensors and (b) the three CS616 sensors (solid lines), assuming a Topp-like soil with a1 = 0.115 and b1 = –0.176 in Eq. [6]. The water content-period relationships according to the factory calibrations for low-conductivity soils are also shown. Note that some of the solid lines representing the individual sensors almost completely overlap.