Top plots: RV measurements of ε Cyg by Kustner (1908) (left), and McMillan et al. (1992), Lick observatory and the SONG telescope (right), along with two orbital models of the binary companion: Fit 1 (black line) is the best-fit solution for the three modern data sets of McMillan, Lick and SONG, with an orbital period of 19 618.6 d; Fit 2 (gray line) was derived from fitting all four data sets and yields a period of 20 175 d. Middle plots: residuals of the RV measurements after removing the orbital solution of Fit 1. The last measurement of Kustner then is a clear outlier. Bottom plots: residuals of the RV measurements after removing the orbital solution of Fit 2. Now all the Kustner RVs agree with the model within their 1σ-uncertainties.