Comparison of the derived values of the rotational speed. Points in the chart represent the measurements for the center of point-like structures with error bars showing the 95% confidence level intervals. The dotted curve shows the fit to the mean ω(b) values as a function of latitude b calculated by Eq. (8). Overplotted are the results of Howard & Harvey (1970) in solid line and Hara (2009) and Brajša et al. (2004) both in the dashed-dotted curve because they are almost identical. Image courtesy of Lorenc et al. (2012).