An Apple Watch a day keeps the doctor away. Some users are astounded by their device’s ability to flag early signs of sickness before an ailment like COVID or a cold arises after the iOS 11 software update rolled out last month. The startlingly accurate health assessment from the Apple Watch’s Vitals app — available on the Series 8 model and above — harnesses critical metrics taken over a week while a user is asleep, according to Mac Rumors. “If multiple metrics are outside your typical range,...