An apparatus for evaluating an earth formation penetrated by a borehole comprising: a two terminal resistivity sensor on a pad, wherein (a) the pad is configured to be proximate to a wall of the borehole; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode, the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes; characterised in that the apparatus further comprises a pair of vertically separated additional return electrodes vertically separated from the at least one current electrode; and wherein the processor determines from a current in the at least one current electrode, and a voltage between the at least one current electrode and the pair of return electrodes, and a voltage between the at least one current electrode and the pair of additional return electrodes a vertical resistivity of the earth formation; wherein the apparatus is configured such that when the measurements are being made with the vertically separated additional return electrodes, the horizontally separated return electrodes are open circuited, and when the measurements are being made with the horizontally separated return electrodes, the vertically separated additional return electrodes are open circuited. a two terminal resistivity sensor on a pad, wherein (a) the pad is configured to be proximate to a wall of the borehole; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode, the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes; (a) the pad is configured to be proximate to a wall of the borehole; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode, the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes; characterised in that the apparatus further comprises a pair of vertically separated additional return electrodes vertically separated from the at least one current electrode; and wherein the processor determines from a current in the at least one current electrode, and a voltage between the at least one current electrode and the pair of return electrodes, and a voltage between the at least one current electrode and the pair of additional return electrodes a vertical resistivity of the earth formation; wherein the apparatus is configured such that when the measurements are being made with the vertically separated additional return electrodes, the horizontally separated return electrodes are open circuited, and when the measurements are being made with the horizontally separated return electrodes, the vertically separated additional return electrodes are open circuited.