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A new support document examines how the Apple Watch measures your heart rate

A new support document examines how the Apple Watch measures your heart rate

That iThingy You're Wearing
April 20, 2015

A recently published Apple support document offers some interesting details on how the upcoming Apple Watch will measure your heart rate.

During workouts, the sensor constantly measures your heart rate. During other parts of the day, it measures heart rate information every 10 minutes. That can be viewed at any time with the Heart Rate Glance on the watch or through the Health app on your iPhone.

The technology behind the sensor is called photoplethysmography. Apple explains more about how it works:

This technology, while difficult to pronounce, is based on a very simple fact: Blood is red because it reflects red light and absorbs green light. Apple Watch uses green LED lights paired with light‑sensitive photodiodes to detect the amount of blood flowing through your wrist at any given moment. When your heart beats, the blood flow in your wrist — and the green light absorption — is greater. Between beats, it’s less. By flashing its LED lights hundreds of times per second, Apple Watch can calculate the number of times the heart beats each minute — your heart rate.

Apple’s watch also uses infrared light to track heart rate information, but will switch to the green LEDs for a more accurate reading, when necessary. Users can also connect a Bluetooth heart rate strap to their watch for better measurement.

To record accurate readings, Apple says the watch should be snug, but comfortable, around your wrist.

Apple is heavily touting the device’s health and fitness features as a major selling point of the watch.

Preorders for the Apple Watch began earlier this month. The first shipment of watches is expected to arrive this Friday, April 24.

Any Apple Watch orders placed today are scheduled to arrive in June or later.

Prices range from $349 for the 38mm Sport model to $17,000 for the most expensive 18-karat gold Apple Watch Edition.

A mid-range Apple Watch collection, with a sapphire display cover and stainless steel exterior, ranges from $549 to $1,099. Apple will also offer a number of other additional bands for the watch.

You’ll need an iPhone 5 or later to interact with the device.

For other news today, see: What you should know about Tidal’s subscription pricing, Don’t expect your Apple Watch to boot up quickly, and HBO sends takedown notices to stop ‘Game of Thrones’ torrents.

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