Comparison of Test Models to the Estimating Functions. Figures displaying the relationships amongst the test data points and the four estimation functions given by equations (2), (3), (4) and (5). These are shown in (i), (ii), (iii) and (iv) respectively. The red lines in each case are given by f
) ± 1 and indicate the boundaries of the regions that are within a factor of 10 of the respective estimations.