Free-Running vs. Entrained Rhythm Simulator

A double-plotted actogram — each row is one day, each day's data repeated on both halves so a run of activity crossing midnight reads as one continuous bar.
Activity onset, day 1:  |  Activity onset, day 20:  |  Drift:
Free-running period used here: 24.5 h/day (a common finding when isolating an animal from all external time cues) — a small daily drift that adds up visibly over 20 days.