The example .stl is for Prague. Insert a latitude, longitude, and local time into equatorial_sundial.scad to generate for a different location.

When oriented north-south facing the equator, the facet edges mark hour boundaries. The geometry also marks equinoxes, solstices, sunrise, sunset, and the Equation of Time (https://www.timeanddate.com/astronomy/equation-of-time.html). The lower set of engraved numbers is Daylight Saving Time for summer.

The attached .3mf includes colored text setup and suggested supports if printing with ASA. (Mine is ASA because UV-resistance sounds useful for a sundial.)

The full repository is published at https://github.com/RyanDMott/equatorial-sundial

This was largely an experiment whether Claude Sonnet 3.5 could write OpenSCAD. I had to change some axes of rotation and such - 3D reasoning is not something LLM's pick up quickly from text - but the components I needed were there.