Relationship between P_cyc and P_rot for the stars in the original sample selected in Paper I and the young solar analogues from Messina & Guinan (2003) (blue squares), together with the fit to the original sample, log P_cyc(obs) = −0.95(±0.16) + 1.21(±0.11) log P_rot, which includes group 2 (except the Sun) and the shorter periods of the stars in group 1. The horizontal error bars cover the range [P_rot(max)–P_rot(min)] derived in Donahue et al. (1996).