Fitness also gets a big push this time around. The Activity app introduces monthly challenges while the Workout app has a simpler Quick Start feature and automatic sets for pool swims. If you're a fan of high-intensity interval workouts, you'll get custom heart rate algorithms. Use connected gym equipment? There's now two-way data transfers to make sure your info is consistent among devices from the likes of Schwinn and StairMaster. And if you're the sort who can't start a run without some music, you can pick a playlist that automatically starts alongside your routine.

There are plenty of tweaks elsewhere. Apple has reworked the dock with an easier-to-use vertical layout, while the Music app is getting an overhaul with a more visual layout and automatic background syncing. Hardware compatibility will be more robust too, thanks to support for Core Bluetooth devices. Your glucose monitor could easily pair to your Apple Watch, for instance.

WatchOS 4 is slated to ship in the fall as a free update. It's not quite the big makeover you saw with watchOS 3, but that's not surprising. Last year's upgrade was about addressing fundamental interface problems: Now it's more a matter of refining the experience.

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