Saw this on a History Chanel show about ancient Egypt. Found an online reference.
It’s a pocket watch of a sundial.
Incredibly simple. Easy to make. For more polar latitudes you would need a ‘seasonal’ line at a bit of a diagonal across it, but hey, technical progress and all that ;-)
It’s basically a long L shaped bit of wood (or whatever). The short leg points up, and that end is pointed toward the sun. It casts a shadow on the long leg. A small plumb bob on the short leg lets you set it to level. At that point, the length of the shadow tells you the time. Near the equator, a single dot would be ‘close enough’ (or a fairly narrow ranging arc) for adjusting for seasons (as the sun wobbles 11 degrees or so each side of straight overhead). At the poles, it will be much more complicated as part of the time the sun is not there at all and at other times it just ‘takes laps’ overhead. In between, a fairly steeply angled line would let you seasonally adjust for the 23.44 degree tilt we have presently. (One could likely put edge marks that would give a pretty good idea of the date when used at rise / set or at high noon, when time, by inspection, could map the adjustment line to a date).
This all means that with a bit of wood, and a stone to mark it with, and maybe a small rock and some plant fiber, you can make a portable ‘watch’ for use when out in the woods. Nice. Very nice.
The picture has a couple of them:
The plumb bob vertical line is visible on the side of image B, even if the bob itself is not there.
Image is from this site:
There is also a very nice write-up about each of these instruments and drawings of how they are oriented to the sun.
Guess what I’m going to be making ;-)
One of them is made of green slate. Another of wood. Wonder if I could make a small metal one and put it on a wrist band ;-)