Colour-period diagram of UBC 1. Left: rotation periods of 17 stars in UBC 1 against Gaia (G_BP − G_RP)₀. Right: comparison of the rotators in UBC 1 (black) with those in NGC 2516 (∼150 Myr, blue) and NGC 3532 (∼300 Myr, orange). Stars in UBC 1 generally rotate slower than those in NGC 2516 while faster than or similar to those of NGC 3532. Crosses in both panels indicate potential binaries in UBC 1.