Logarithm of cycle periods on the short-cycle branch versus the logarithm of the Rossby number. Upper panel: Cycle period against Rossby number for cycles on the short-period (inactive) branch; different colours and symbols indicate the different B − V ranges. The solid-coloured lines show the respective empirical relations, with colours indicating the different B − V ranges. Lower panel: Relative deviation () versus the logarithm of the Rossby number. The green points label the stars within the B − V range of 0.5 < B − V ≤ 0.6, the red points stars within 0.6 < B − V ≤ 0.7, and the black points those within 0.7 < B − V ≤ 1.1.