Parameter e_P (left panels) and its comparison with previous statistical parameters (right panels) as a function of the number of measurements (see Table 1). The colours and symbols are the same as those adopted in the Fig. 1. In the left panels the results for the full range of measurements are used, while the right panel only shows those for odd numbers of measurements except for EIQR, where only the results with numbers of measurements that are not modulus 4 are plotted. The solid lines in the even-dispersion diagrams show the models described in Sect. 5.3.