Top left: a typical transverse displacement of one pixel along the loop segment ( + ), joined together using a spline fit to assist visualisation of the motion path (solid line). Top right: the original transverse displacement ( + ), overplotted with a 501 s period sinusoidal signal (dashed line). Bottom left: the residual (501 s period sinusoid subtracted from the original motion path) transverse displacement ( + ), overplotted with a 274 s period sinusoidal signal (dashed line). Bottom right: the original data points ( + ) and spline fit (solid line) shown in the upper-left panel, overplotted with the combined 501/274 s period sinusoidal fits. These combined fits, with respect to the original time series, result in Kolmogorov-Smirnov and cross-correlation statistics of 92% and 98%, respectively, indicating a high degree of accuracy.