Christiaan van der Klaauw Astrolabium

I’m unsure how the mechanics of this beauty work, but they’re set to have the moon overtake the sun at month’s end whereas the “horizontal serpent” icon is frozen in place because I could not determine its function. The current month is at 12 o’clock and the zodiacal signs are a mystery. Here is a link to an animation of the real watch that doesn’t answer all my questions: perhaps a forum member can figure it all out (Christiaan van der Klaauw CK Astrolabium - YouTube) .