How were the circles drawn?

[Jorge_Stolfi]

In the image in  Codex Vindobonensis 2554, f.1 verso , you can it on the wikipedia page Bible moralisée  circa 1220 CE

Wow, fantastic! Thanks!

Actually that point looks more like the modern implement (minus the adjustment screw) than like a metal pen.  The two prongs are clearly separated at the top and come together only at the lower tip. 

By the way, many details of that diagram resemble details in the VMS illustrations, especially in the Cosmo pages:

• Stars with slender rays and a core with a circle and dot at the center (e. g. f68r2).
  
• Stars with long wavy rays (e.g f68v2).
  
• The "dendritc" water edge (cf f68v3).
  
• A "cloud-shaped" land mass at the center (cf f57v).
  

The Scribe and/or the Author were obviously aware of the "graphical language" of European scribes at the time.  In particular they seem to have been aware of the "alchemical herbals" (was there more than one?), zodiac depictions, and possibly balneological catalogs.  

Yet the deep source of the VMS, below the surface of those "graphical idioms", does not seem to be "standard fare" at all. Or is it?

All the best, --jorge