Variations of (left) the minimum angular distance to the auroral oval, δ, and (right) the scalefactors, s(δ), for the aa stations. The colours used are as in Figure 4 (namely mauve for Greenwich, green for Abinger, red for Hartland, black for Melbourne, cyan for Toolangi and blue for Canberra). The thin lines are the variations shown in Figure 4 and the thick lines are constant values used in generating the classic aa. The dot-dash lines in the right-hand panels show the reciprocals of the standard multiplicative correction factors and the thick lines the factors corresponding to the constant δ values in the left-hand panels.