The study investigates the rotation of the Earth's inner core (IC) by analyzing seismic waveforms from repeating earthquakes and explosions. By compiling 143 pairs of such events recorded on medium-aperture arrays in northern North America, the researchers document that many multiplets exhibit waveforms that change and then revert to match earlier events. This reveals times when the inner core re-occupies the same position relative to the mantle, indicating super-rotation from 2003 to 2008 and sub-rotation from 2008 to 2023. The pattern of matches, combined with previous studies, demonstrates a reversal in IC rotation direction and a significant slowdown in the latter period. The findings provide precise and unambiguous tracking of inner core progression and regression, suggesting that new models are needed to understand the dynamics between the inner core, outer core, and mantle. The study also highlights the complexity of IC motion, which is more than a symmetric function like a sinusoid, and the need for further research to monitor motion in this enigmatic region.The study investigates the rotation of the Earth's inner core (IC) by analyzing seismic waveforms from repeating earthquakes and explosions. By compiling 143 pairs of such events recorded on medium-aperture arrays in northern North America, the researchers document that many multiplets exhibit waveforms that change and then revert to match earlier events. This reveals times when the inner core re-occupies the same position relative to the mantle, indicating super-rotation from 2003 to 2008 and sub-rotation from 2008 to 2023. The pattern of matches, combined with previous studies, demonstrates a reversal in IC rotation direction and a significant slowdown in the latter period. The findings provide precise and unambiguous tracking of inner core progression and regression, suggesting that new models are needed to understand the dynamics between the inner core, outer core, and mantle. The study also highlights the complexity of IC motion, which is more than a symmetric function like a sinusoid, and the need for further research to monitor motion in this enigmatic region.