Comparison of LBL RVs data for GJ 251 with and without zero point correction. The top panel shows the data with and without zero point correction, indicated by black and red points respectively. The zero point offset is shown in blue. The bottom panel shows the corresponding periodograms for the time series in the same color scheme, and the blue line represents the window function. The significance levels of FAP = 10⁻³ and FAP = 10⁻⁵ are indicated by the solid and dashed horizontal lines, respectively. The 1-yr period, the 180 days period, and the synodic (29.5 days) period of the Moon are represented by vertical black dashed lines, and the period of the claimed planet in Stock et al. (2020) is in red.