Our harmonic classifier enables reconstruction of open cluster rotation–temperature sequences. Left column: rotation period–effective temperature sequence for the Pleiades (t ∼ 120 Myr), Praesepe (t ∼ 670 Myr), and the Hyades (t ∼ 700 Myr). We adopt membership lists for each cluster from E. L. Hunt & S. Reffert (2023). Literature rotation periods are taken from L. M. Rebull et al. (2016) for the Pleiades, R. Rampalli et al. (2021) for Praesepe, and S. T. Douglas et al. (2019) for the Hyades, and are marked in gray. Green points indicate TESS measurements with P(match) > 0.8, and yellow points denote measurements with P(harmonic) > 0.8. A clear secondary sequence at approximately half the literature period is visible in Praesepe and the Hyades for 3500 ≲ T_eff ≲ 6000 K, and the majority of stars on this sequence are correctly identified as harmonics. Right column: the adopted periods for each of these stars from the default TARS catalog, colored by the uncertainty on the period. Our harmonic flagging and doubling procedure allows us to correct harmonics and recover rotation periods that closely reproduce the literature rotation sequences.