A nocturnal, also known as a star dial, is an analog computer used for telling the time using the relative positions of stars in the night sky.

Reference stars:

• Pointer stars of Ursa Major
• Kochab of Ursa Minor
• Shedar of Cassiopeia

To operate:

• Spot one of the reference stars and align the relevant constellation on the inner ring with the current date on the outer ring.
• Sight the North star (Polaris) trough the center hole
• With the handle pointing down, align the Pointer with the chosen reference star
• The Pointer now intersects the current time on the inner ring!

NB - The customizer app seems to return an error while rendering the more complex components (Inner and Outer Rings), I'm looking into this problem but for now I have uploaded STLs for the 'Spiral' style nocturnal, and you can still customize by downloading the OpenSCAD file.