A six-sided device that can tell you the moon phase for any date and time in the previous or future 8,000 years.
They also have flat versions.
And a how-to-figure-it-out-yourself (approxmiately: in your head if you’ve got an excellent memory or exactly: with a calculator) writeup.
I would love to play with the six-sided version. I’m sure I could waste hours trying to figure out how it works. There is an image of each side — maybe I can make my own out of paper…
