An electrode device with small spacings from which the current flow, and hence the measurement, is focused a short distance into the formation. The proximity log measures the resistivity of the flushed zone with minimum influence from the mudcake or the undisturbed zone. The central current-emitting electrode (A0) is surrounded by a guard electrode that emits sufficient current to focus the current from A0 a certain distance into the formation. The electrodes are mounted on a pad that is pressed against the borehole wall. In a typical tool design, 90% of the signal comes from within 5 to 10 in. (13 to 25 cm) of the pad. This is deeper than the microlaterolog, which ensures that the mudcake has less effect but means that the proximity log is more often affected by the undisturbed zone.