The Science of Watch Rotation

After 17 hours awake, cognitive impairment equals a blood alcohol of 0.05%. After 24 hours, it reaches 0.10% (Dawson & Reid, 1997, Nature) — legally drunk in every country. Watch rotation isn't about fairness. It's about keeping impairment below the threshold where people stop noticing their own mistakes.

The worst schedule isn't the one with the shortest watches. It's the one where the same person always gets the 0200–0600 slot — the circadian trough where reaction times double and change blindness peaks.