Example of a cycle period categorised as CB (HD 20630). The top plot shows the data in black circles. The red curve is the fit to the two strongest peaks in the periodogram shown in the bottom plot. The shaded grey area shows the span of the solar chromospheric activity from minimum to the maximum, shifted to the centre at the star’s mean value. The dashed horizontal line shows the mean of the data points. The two strongest peaks are marked by the dashed red and blue lines in the bottom plot.