“I’ve been on the phone four times, for an average of 24 minutes a call. my last phone call was 22 minutes 23 seconds long … My average mile when I ran 5K yesterday was 8 minutes and 45 seconds … I am exactly 45 percent through my friend’s excellent nonfiction book … My optimal sleep time is seven hours and 20 minutes and I wake up twice a night.” Welcome to the age of self-quantification. New technologies are making it easier for us to measure every detail from our waking — and sleeping — lives. Newsweek’s Alissa Quart wonders whether all that tracking is good for our health.