Those old sundials are just too difficult to tell time on, aren't they?
Technologically, it isn't what we normally think of as digital, not using electrical power or circuits - it has no moving parts (though it does use digits, so the word is accurate). Just two light filtration masks that cause different numbers to shine through depending on the angle of the sun as it hits the device.
Here's the thing, though - at a cost of 91 Euros, it's a helluva lot pricier than a watch. So I'll just go ahead and file this under "Cool but Kinda Pointless."