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Swinging about an anchor under the force of wind or currents would tend to make a circular arc.

Normally back and forth on the downwind or down-current side of the circle, though. The chart shows it completing several circles.

The chart shows most of the data points on a small portion of the arc.

Reversals are completely normal for cyclic tidal currents or sea breeze / land breeze cycles.

Same for tides.