I had the idea of making a Salvador Dali-inspired design with an irregular shape when I was working on this one, but I didn’t have the energy…=)

The in- or outward motion of the hand could be read from the guide groove. If the wearer knows in what direction it rotates, it’s very easy to tell. The groove might also have tritium markings, to make it as readable as the rest.

Friction might conceivably be an issue, yes. However, the hand would be very light and wouldn’t be able to cause enormous amounts of it. It’d need solid engineering to avoid making it too power-hungry. though… Judging by what they’ve managed in the past, I’m sure the TF boffins would be able to sort it very nicely.=)
you might use a piezo-electric motor, come to think of it. That should sort any friction trouble…

If my mental arithmetic is what it should be, then you wouldn’t need a terribly custom movement. The minutes work as on any other watch, and the guide groove needs to be geared to rotate one revolution more than the minutes per 24 hour period.

Actually, I didn’t think about the record player connection before you mentioned it…=)
I think someone submitted one like that some time ago… Can’t remember who it was, unfortunately…
If I were to do something like that I’d probably like to put the arm outside of the ‘record’, to really go with the analogy…

Comment:
> Ander, what you’ve designed is 100% original as far as I’m aware. I’m not an expert, but I spend a lot of my leisure time learning about watches. I’ve seen single hand watches and I’ve seen watches that have extending and receding hands. I’ve never seen a single hand watch that used a minute hand rather than an hour hand. I think that that’s unique. I’ve never seen a watch that uses the extending of a hand as part of the display. The watches with extending hands I’ve seen have that feature because the watch face has an irreguglar shape.
Questions:
>How do I know if it’s 11:04pm instead of 1:04am? I understand that outward and inward motion of the hand indicate am & pm, but I can’t see the hand moving at any particular moment.
>I have one concern about the sliding hand. Have you thought about friction? If it were a mechanical watch rather than quartz, then this would be a much more serious concern, but I think it still it’s worth considering. I don’t know how much resistance a battery operated watch can tolerate, but it stands to reason that there’s some upper limit which would stress it enough to cause damage. After all, they’re designed to use as little energy as possible and usually the hands are swinging free. I know that if you’re building a clock with heavy arms (either because they’re very long or very ornate) it’s best to get a high torque movement to deal with the added weight. It would seem that having the arm dragged by the guide might raise the same sort of issues.
Observation:
>You won’t be able to use a standard movement. You’ll need a specialized one designed for 24 hour analog dials with a 24:1 reduction gear train to turn the disk with the guide on it rather than a standard 12:1.
Suggestions:
>You could add a day/night indicator to distinguish between the outward and inward (am & pm) hours.
>Surely you’ve noticed how much your design is reminiscent of an old fashioned record player (phonograph). I’m not old enough to have ever bought records, but my parents used to play records when I was growing up. The black minute indicator with all of the concentric hour circles looks like an LP. The hand looks like a tone arm, and tone arms had to move inward as the needle went from the outside toward the center of the record. Your hand is being dragged inward (and outward) by a “needle in a groove” too. Why not call your design the Needle&Groove watch?

http://upload.wikimedia.org/wikipedia/commons/5/52/German_-_Spherical_Table_Watch_%28Melanchthon%27s_Watch%29_-_Walters_5817_-_View_C.jpg

From Wikipedia, “1500–1600 Clock-watches: The first timepieces to be worn, made in the 16th century in the German cities of Nuremberg and Augsburg, were transitional in size between clocks and watches. These ‘clock-watches’ were fastened to clothing or worn on a chain around the neck. They were heavy drum shaped cylindrical brass boxes several inches in diameter, engraved and ornamented. They had only an hour hand.”

Clocks began to have minute hands in the late 1400′s, but it was much later when they were added to watches

It’s worth looking back at how watches evolved. One handed watches are actually the oldest kind that there are. When watches were first being made, adding a minute hand required an extra level of complexity to the movement which was difficult given that making very small precise gears was the cutting edge of technology. Also, bear in mind that these early watches were not wristwatches, but much larger pocket watches since they couldn’t make works to fit into cases any smaller. Every added ‘complication’ made a watch (or a clock for that matter) harder to build, so the two hand watch is newer and the second hand newer still. Later we got calendar, moon phase, chronograph, and a whole lot of other fancy additions which watchmakers added to show their technical proficiency. Moreover when you go that far back in history, most people didn’t really need a minute hand. If you were a navigator, or later on a train conductor, it would matter, but most people did fine with knowing it was nearly a quarter past five rather than 5:13 or 5:14.

So, you’re right that a single hand isn’t new. It’s as old as watched themselves, but single handed watches have always had the *hour* hand as the single hand. Ander has a single minute hand. That’s new as far as I know.