Example phase-folds using FRB 20180916B at 32.56 days with different bin numbers and phase-origin shifts. For each sub-figure, the top figure is the histogram of observed bursts (solid blue) and uniform expectation (dashed green) in each phase bin with the residue displayed in the bottom figure. The χ² metric is proportional to the sum of the squared value of this residue. The grey span in the histogram shows the inactivity fraction (F₀).