Earth’s J₂ values evaluated from SLR and its long-term variation. The constant ${\overline{J}}_2$ is the mean value for J₂, which equals 0.0010826359797. The original data with continuous updates to 2025 are provided by Cheng et al. (2013). The error bars are shown in gray. The green dashed line indicates the endpoint of the data that were used in LC17. The linear and parabolic fits within different time intervals are shown as colored curves.