FitBit’s measurements of my quantity and quality of sleep became a kind of empirical assurance, a metrical safety blanket that said, “Yes, you can feel this tired,” or “You should feel spry and alert.” Does it know better than I do how much sleep I got, or how tired I should feel? Does it matter if these measurements are actually accurate? What would "accurate" even mean when it came to how I felt? How did I come to implicitly trust it over my own consciousness?