The two variants of the new Apple Watch have the same face sizes as last year's models, though Series 2 does come in at 9 percent thicker.
The new models are a little heavier too, but this isn't likely to be noticeable on wrist.
The only build difference between Series 2 and the original Apple Watch is that the Apple Watch Edition, which used to be a US$10,000 luxury for the Beyoncés and Drakes of the world, now trades 18k gold for ceramic, and gets a much less hip-hop-idol-worthy $1,249 starting price.
But new "Series 1" Apple Watch, which is slightly different from the original Apple Watch, is only sold with the aluminum casing.
Band compatibility is identical for both watches.
No changes here this year, as the two Apple Watch sizes keep the same screen sizes.
Ditto for resolution. Standing pat.
Apple also stuck with OLED display panels in the new model.
The entry-level Sport watches still have Ion-X glass displays (similar to Gorilla Glass), while steel and Edition models jump up to sapphire.
Apple says the new Apple Watch's display gets twice as bright (1,000 nits max) as the original's. That could help you to better read your latest iMessage or track your Pokémon Go hunt in bright outdoor settings.
One of the big things helping Apple to keep the Watch's size down may be its reluctance to add an always-on display option, something (usually much bigger) Android watches have been doing for years.
The Force Touch feature (that later evolved into 3D Touch on the iPhone) is back in Apple Watch 2.
This is one of the big upgrades in the new Apple Watch, as Series 2 is water-resistant up to 50 m depths – and gets some new software to track swims and surfing.
Some earlier rumors had suggested Apple would build 3G or LTE data into the Apple Watch, to let you truly leave your iPhone at home, but that didn't make it into the 2016 model.
You can, however, leave your phone at home while on jogs, and still track your trek with the Series 2 Watch's built-in GPS.
Apple is quoting the same "up to 18 hours" estimate in Series 2, despite the addition of GPS.
This explains the slightly thicker and heavier builds in the new models: GPS requires a bigger battery to maintain (allegedly) same battery life.
The Apple Watch 2 switches to a dual-core chip, from the original's single core, to help speed things up.
But this is another category where "Series 1" differs from the original Apple Watch. The latter had a single core chip, while Series 1 goes dual core.
Heart rate sensor
Like most smartwatches, both series have pulse sensors.
Of course the Apple Watch still works exclusively with iPhones.
Sorry, Android phone owners, you'll need to pick up something like a Gear S3 if you want a smartwatch to go with your handset.
Apple is partnering with Nike for a special model of the Series 2 Apple Watch with Nike branding and a special running app (complete with nags to guilt-trip you into slogging out for a jog).
The original Apple Watch will soon be running the new watchOS 3 that Series 2 will ship with.
The new model launches about a year and a half after the first (and two years after the original Apple Watch was announced).
The asterisk there denotes the fact that the Series 1 Apple Watch is, again, technically a different watch from the original. So to be as technically correct as possible, we'd say Series 1 launched in September of 2016, while the original Apple Watch hit store shelves in April of 2015.
The Series 1 Apple Watch has seen numerous price drops at retailers for much of the past year, but now a $100 drop below the new model is official.
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