The arrows on Method are drawn today as a stroked shaft with a separate filled triangle, which is why the two never quite agree at the neck. This is the bench for replacing them: the same four numbers coylean-map's arrow tester used — SW the shaft half-width, HL the head length, HW the head half-width, ND the notch where the head meets the shaft — plus a MARGIN pulling both ends in off the vertex dots. Every number is a fraction of the rhomb edge, since that is what the canvas works in.
The arrows are unidirectional. “Double” and “single” name de Bruijn's two markings, not a count of heads: an edge carries one arrow either way and the color is the whole distinction. Both ends are pulled in by the margin — the tail’s round cap and the head’s tip alike — and at a margin equal to the vertex mark’s radius the point lands exactly on the circle round the index, which is what stop at the mark sets. The mark itself is drawn, so you can see whether it does.
The pattern is not invented here: rhombArrows is imported, so the
doubles and singles fall where the tiling puts them — doubles into the
extreme corner, singles opposite, out of it on a thick and into it on a thin.
The stage shows before and after together: the stroked shaft with its
separate triangle as the page draws it today, over the single outline that
would replace it.
Temporary. A bench, not a page of the site: it exists to
settle the arrow's shape and colors, and what comes out of it belongs in
drawColoredArrows. The Legacy preset and the
before only shape are kept deliberately — they are the drawing
that was replaced, so it can be compared against and brought back. Note that a
preset’s MARGIN is the bench’s own: the view drives it from the
vertex mark in pixels, since a mark is the same size however far you zoom, and
a constant fraction of the edge is right at exactly one zoom.