A method of measuring earth ground resistivity comprising the steps of: providing a testing device including a main unit (I, MU) and a portable remote unit wherein said portable remote unit is removably coupled with the main unit and adapted to communicate with one another via a communication link; electrically connecting said main unit of said testing device to at least two electrodes (A,B, X,Z) placed in the ground at a predetermined distance from one another; said testing device: generating a predetermined current between said at least two electrodes; measuring a drop in voltage potential values using one or two probe(s) (M,N, Y) between said at least two electrodes; calculating resistance values based on said predetermined current and said measured drop in voltage potential values; and displaying any of said values on said portable remote unit for viewing by an operator, wherein the portable remote unit is electrically connected to said one or two probe(s) (M,N, Y) for measuring voltage or to a current sensing clamp for measuring current so as to enable calculation of said resistance values, and wherein: when said portable remote unit is electrically connected to said one or two probe(s) (M,N, Y) for measuring voltage, the one or two probe(s) is(are) placed in the ground in a current path between said at least two electrodes (A,B, X,Z), directly between said at least two electrodes or at an angle to said at least two electrodes; and when said portable remote unit is electrically connected to the current sensing clamp, the current sensing clamp is placed around one of said at least two electrodes place in the ground. providing a testing device including a main unit (I, MU) and a portable remote unit wherein said portable remote unit is removably coupled with the main unit and adapted to communicate with one another via a communication link; electrically connecting said main unit of said testing device to at least two electrodes (A,B, X,Z) placed in the ground at a predetermined distance from one another; said testing device: generating a predetermined current between said at least two electrodes; measuring a drop in voltage potential values using one or two probe(s) (M,N, Y) between said at least two electrodes; calculating resistance values based on said predetermined current and said measured drop in voltage potential values; and displaying any of said values on said portable remote unit for viewing by an operator, wherein the portable remote unit is electrically connected to said one or two probe(s) (M,N, Y) for measuring voltage or to a current sensing clamp for measuring current so as to enable calculation of said resistance values, and wherein: when said portable remote unit is electrically connected to said one or two probe(s) (M,N, Y) for measuring voltage, the one or two probe(s) is(are) placed in the ground in a current path between said at least two electrodes (A,B, X,Z), directly between said at least two electrodes or at an angle to said at least two electrodes; and when said portable remote unit is electrically connected to the current sensing clamp, the current sensing clamp is placed around one of said at least two electrodes place in the ground. when said portable remote unit is electrically connected to said one or two probe(s) (M,N, Y) for measuring voltage, the one or two probe(s) is(are) placed in the ground in a current path between said at least two electrodes (A,B, X,Z), directly between said at least two electrodes or at an angle to said at least two electrodes; and when said portable remote unit is electrically connected to the current sensing clamp, the current sensing clamp is placed around one of said at least two electrodes place in the ground.