Apparently I Slept Terribly Last Night. Shame Nobody Told My Body.
For most of my adult life I have known exactly how well I slept within about four seconds of waking up. No instrumentation required. I would open one eye, assess my willingness to speak to another human being, and issue a verdict. Good sleep: cheerful, borderline insufferable. Bad sleep: monosyllabic, dangerous to approach before coffee. This system had a sample size of roughly fifteen thousand nights and, as far as I could tell, a fault rate of zero.
Then I strapped a small black rectangle to my wrist and let it start marking my homework.
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