This engineering wonder merges ancient technology with the most modern.Thingiverse member Mojoptix designed a sundial that displays the time in 20 minute increments from 10 AM to 4 PM.
How does it work? The gnomon is perforated with holes that display the numbers only when light shines from particular directions. You can download the files here and print your own.
In this video, Mojoptix explains at length how sundials work and how he designed this one. He wrote a program that calculated where the holes had to appear in order to direct light correctly. The body is printed with Utilimaker 2 3d printer.