Upper frame: a sample nightly light curve, at 24 s/point. A nine minute pulse of varying amplitude is visible. In retrospect, the amplitude changes appear to be almost entirely caused by the beating of the signals closely spaced in frequency. Lower frame: average power spectrum of the eight best nights, revealing periodic signals, flagged with their frequency in cycles/day (with  ± 0.2 errors). The broad excess of power near 155 c/d is entirely owing to the varying power-spectrum window of the eight nightly time series.