  A new prediction technique based on logarithmic values is proposed to predict
the maximum amplitude (Rm) of a solar cycle from the preceding minimum aa
geomagnetic index (aamin). The correlation between lnRm and lnaamin (r = 0.92)
is slightly stronger than that between Rm and aamin (r = 0.90). From this
method, cycle 24 is predicted to have a peak size of Rm (24) = 81.7(1\pm13.2%).
If the suggested error in aa (3 nT) before 1957 is corrected, the correlation
coefficient between Rm and aamin (r = 0.94) will be slightly higher, and the
peak of cycle 24 is predicted much lower, Rm(24) = 52.5\pm13.1. Therefore, the
prediction of Rm based on the relationship between Rm and aamin depends greatly
on the accurate measurement of aa.
