The bioengineer Takuo Aoyagi died in Tokyo in April, around the same time that people began clamouring to panic buy his 1970s invention, the pulse oximeter. Blood oxygen saturation, which pulse oximeters measure by transmitting red and infrared light into, say, your middle finger and comparing how much of each is absorbed by the blood, is considered one of five valuable vital signs, alongside...
Why can’t your fitness tracker tell you if you have coronavirus?
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