The characteristics of the fourth curve are described the three electrodes method which is one of the methods of the electrical coring The author plains the thecretical. equations for three layers by use of the elccirc images and calculates the theoretical curves in the case of the formation witch is the cthickness is less than six times pick-up span. And the distance between the potential electrodes can describe the variations in the thin layers chiefly in order to calcula e the forth curve the spacing is 4.5 times pick-up spani the curves are indicated at Figure 2 and 3
