Let’s pay a visit to the Department of Awesome Antiquities and take a look at a 17th century pocket watch, courtesy of Columbia University. This astonishing device is a sort of sundial called a diptych dial, used for telling time by the light of the sun or the moon. They were produced by exceptionally skilled craftmen, most often in Nuremberg, Germany, from the 1500s through the 1700s.
"When opened, the string gnomon—the raised device that creates a shadow—is drawn tight. On some more sophisticated models, the string can be adjusted to account for different latitudes. Typically the top section would be used to determine the time using sunlight and the bottom section would be used to learn the time with moonlight."
This exquisitely beautiful Diptych Dial was created by Hans Trvschel in Nuremberg in 1603. It’s made of ivory, with a string gnomon horizontal dial and pin gnomon for the vertical dial.