The best new feature for the Apple Watch proves Apple is serious about fitness tracking

When Apple unveiled the new Apple Watch operating system at its annual developer conference on Monday, it was clear that the focus is on fitness.

WatchOS 4 offers new workouts like high-intensity interval training, personalized notifications to help you stay motivated, and the option to have your playlists start as soon as you begin a workout.

But arguably the coolest new feature is the launch of GymKit, which allows you to pair your Apple Watch with your gym equipment to more accurately track your workouts.

Using an NFC reader, your Apple Watch will be able to sync with a treadmill or elliptical machine to track things like calories, distance, speed, floors climbed, incline and pace. While both the watch and the machine already do most of these things on their own, they don't always do them accurately - the watch might be better at tracking calories, for instance, but the treadmill may be able to give a more accurate distance reading.

Brands like LifeFitness already allow you to sync your equipment with an app on your phone to better track your workout. But integrating an NFC reader directly into a cardio machine is new, as is the ability to pair it with your watch with one tap.

If you've ever tried to track your indoor workouts, you may have noticed some discrepancies between what your fitness tracker tells you and what the treadmill tells you, and it can be hard to tell which one to listen to. The new technology will hopefully eliminate that confusion and make for better workouts for both fitness buffs and beginners alike.

Apple is partnering with LifeFitness, StairMaster, Schwinn, and a few other makers of cardio equipment to add the technology into their machines, but it likely won't start showing up in gyms until this fall.