Absolute value of the surface shear coefficient α_DR as a function of the rotational period for spotted stars (Kővári et al. 2017). Single stars are indicated by circles, and those in binary systems are denoted by filled symbols. EK Dra is marked in red. The dotted line shows a linear fit to single stars with a slope of |α_DR| ∝ 0.0049 P_rot[d], the lower slope of the dash-dotted line is |α_DR| ∝ 0.0014 P_rot[d], and it is fit to stars in binary systems (Kriskovics et al. 2023).