The new Apple Watch Series 6 includes a sensor that allows the watch to measure blood oxygen levels. The device is a long-awaited addition to Apple’s suite of health tools, but it tracks oxygen levels at the wrist, which can be less accurate than measurements typically gathered at the fingertip.
Most oxygen sensors, including Apple’s, measure the amount of oxygen in your blood using light. These devices are called pulse oximeters, and they typically clip on to your fingertip. A standard version sends both red and infrared light through the finger, where there’s lots of blood close to the surface. A protein in the blood absorbs more infrared light when it has oxygen and more red light when it’s doesn’t. A sensor on the other side of the…