Yearly sunspot group number of von Lindener (red diamonds), Derfflinger in his summary manuscript (blue circles: Hayakawa et al., 2020b), Prantner (blue diamonds: Hayakawa et al., 2021a), and Tevel (orange squares: Carrasco, 2022). For reference, these data are compared with the annual sunspot group number of Chatzistergos et al. (2017), which has been regarded as “the most recommendable version for further analysis” in Petrovay (2020, p. 11). Accordingly, we have calculated the error margins for the individual data series in a standard error, whereas we have derived the error margins of Appendix B in Chatzistergos et al. (2017).