The van der Pauw Method is a technique commonly used to measure the Resistivity and the Hall Coefficient of a sample. A correction factor goes into calculating the resistivity as described in van der Pauw paper. A iterative method is generally used to calculate the correction factor and this correction factor is plotted in Figure 5 of van der Pauw paper
This figure was produced by the octave code shown below. The raw data is here.
% Fore more details see the paper L. J. van der Pauw, A method of measuring the resistivity and hall coefficients of Lamellae of arbitrary shape, Philips Technical Review, Vol 26, 220.
x = logspace(0,3,100);
F(i) = fsolve(Lp,0.5);
ylabel('Correction Factor (f)')
title('van der Pauw Correction factors for resistivity measurements');