Illustration of changing characteristics of signals in RV, RV residual, and activity index data of GJ 3942. It is grouped into seasons 1 & 2 (S12, green dots), season 3 (S3, red dots), and season 4 (S4, black squares). The best purely sinusoidal fit for each dataset is shown. Panel a shows the RV data folded in phase with a 16.29-day period; panel b the residuals after correcting for the best sinusoidal 16.3-day period fit and phase folded with 6.91 days; panel c the S index data folded in phase with a 16.26-day period; and panel d the Hα index data phase folded with 16.25 days.