Last call: back cover. It's press-fit over a teflon-like O-ring, but a thumbs-up and a firm push relieves it of duty.

The material has been standardized across watch models and souped up to snazzy ceramic, replacing the previous Ion-X or Sapphire options.

It also houses the PPG sensor array that is responsible for sensing heart rate.

It would've been cool to see some change from the Series 2 after complaints about accuracy in previous models. As far as wearables go, however, the Apple Watch is the best of the bad.

Also it appears that the wireless charging coil has been slightly modified to support most Qi wireless chargers.

Lastly, with the new barometric altimeter taking the spot next to the microphone, where did the air vent go? Answer: hiding out right here, next to the diagnostic port.