Placidus, Koch, and the rest. What they do differently, and why this site does not use them.

This page is a seed. The full write-up is coming; for now it exists so the links that point here resolve, and so the shape of the codex is visible while it grows.

what belongs here

  • the plain-language definition
  • why it matters for reading a chart
  • the common beginner misreading, and the correction
  • where it shows up in practice