An oil and gas exploration method comprising: performing a first measurement including measuring an electromagnetic field at a first sensor at a first position and measuring the field at a second sensor at a second position; interchanging the first sensor and the second sensor such that the first sensor is at the second position and the second sensor is at the first position; performing a second measurement including measuring the field at the first sensor at the second position and measuring the field at the second sensor at the first position; the method being characterised in that it further comprises: using the first measurement and the second measurement to reduce electronic errors and/or sensor errors in measuring the field, a difference in the field, or a combination of the field and the difference in the field, and wherein the method includes: generating, from the first measurement, a first difference between the measured field at the first position and the measured field at the second position; generating, from the second measurement, a second difference between the measured field at the first position and the measured field at the second position; and combining the first difference and the second difference. performing a first measurement including measuring an electromagnetic field at a first sensor at a first position and measuring the field at a second sensor at a second position; interchanging the first sensor and the second sensor such that the first sensor is at the second position and the second sensor is at the first position; performing a second measurement including measuring the field at the first sensor at the second position and measuring the field at the second sensor at the first position; the method being characterised in that it further comprises: using the first measurement and the second measurement to reduce electronic errors and/or sensor errors in measuring the field, a difference in the field, or a combination of the field and the difference in the field, and wherein the method includes: generating, from the first measurement, a first difference between the measured field at the first position and the measured field at the second position; generating, from the second measurement, a second difference between the measured field at the first position and the measured field at the second position; and combining the first difference and the second difference. using the first measurement and the second measurement to reduce electronic errors and/or sensor errors in measuring the field, a difference in the field, or a combination of the field and the difference in the field, and wherein the method includes: generating, from the first measurement, a first difference between the measured field at the first position and the measured field at the second position; generating, from the second measurement, a second difference between the measured field at the first position and the measured field at the second position; and combining the first difference and the second difference. generating, from the first measurement, a first difference between the measured field at the first position and the measured field at the second position; generating, from the second measurement, a second difference between the measured field at the first position and the measured field at the second position; and combining the first difference and the second difference.