design the test device 200 such that the lateral distance w is relatively small in comparison to the length l in order to reduce errors due to current losses for example a 1 mm lateral distance of a 1 mm by 1 mm probe may have the same current losses as a 2 ft by 2 ft probe similarly a 1 mm by 10 mm probe may have the same current losses as the 1 mm by 1 mm probe because the lateral distance w is the same width and the current is allowed to flow around two ends but the error due to the current losses gets divided by 10 when the correction is applied in a particular aspect of the invention the geometric correction for a probe with parallel and equal length conductive members is the lateral distance w divided by the contact length l i e w l preferably the outer and inner conductive contacts 206 207 of each pair 204 205 may be substantially parallel similarly the first and second pairs 204 205 may also be substantially parallel with each other such parallelism of the conductive contacts 206 207 may simplify the process of data reduction and may improve measurement accuracy if the conductive contacts 206 207 are non parallel however the non parallelism may be measured and accounted for in the data reduction algorithm furthermore the contact lengths l of all of the.