Like the ones in the white box on the table that you can touch? Did they have one on the back or is the power going thru the band?

Like the ones in the white box on the table that you can touch? Did they have one on the back or is the power going thru the band?
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Gunk likes to accumulate inside "safe havens", not on exposed, rubbed and washed surfaces. As I said, we'll see...
They might get rid of it for the retail units, I wouldn't count on the store displays being what ships in a couple weeks.
Right, they are showing up on the videos that were probably made weeks ago, and are showing up on demo units in stores. Those are not retail units. As you said, they are probably using that port to at least power the demo units, so they could very well be specially made for that purpose, and the ones for trying on aren't functional but running a demo loop.It's pretty final at this point. It shows up in their materials promo videos (for the Edition model, no less):
https://www.macrumors.com/2015/03/09/apple-watch-diagnostic-port-spotted/
It shows up on the watch try-on models if you take the band off, and the explorable mounted display model with the running OS is functional, screen-on, all day in the store, without a magsafe charging puck underneath. They are probably powering it through that port.
Right, they are showing up on the videos that were probably made weeks ago, and are showing up on demo units in stores. Those are not retail units. As you said, they are probably using that port to at least power the demo units, so they could very well be specially made for that purpose, and the ones for trying on aren't functional but running a demo loop.
We won't know if retail units have this port until the 24th.
Port is probably the wrong word, since a port would be a water problem. It is just pin connectors. They are probably USB.
EDIT: It is not USB since USB is only 4. I bet it is a Lightning interface. This way Apple has proprietary use and no one else can use it for nefarious reasons (like Jailbreaking).
Gruber's review unit has the port with a small metal cover over it.
Right, an early review unit they got at least a couple weeks ago. Not a retail unit. Apple even announced that retail units would be different from review units (they wouldnt have as much lag)