No text, but a visual code

[Rafal]

but in reality, it is not a clock but a small volvelle—a medieval tool used for astronomical and astrological calculations.

What is your proof that it is a drawing of a volvelle? Not a clock, not a sigil and not some meaningless ornament?

Can you show some similar drawings of volvelles (not actual, moving volvelles but drawings of volvelles) in other sources as a reference?