When I first analyzed versions of script designs Jurriaan Schrofer developed for his second proposed Dutch passport (1972–73), I overlooked the details of an alternate method he explored for adjusting the weight of the glyphs. That was in part because the diagrams for them he included in Letters op maat didn’t include them.
It wasn’t until I translated his designs into code (Python, in DrawBot) that it became clear to me just how sophisticated the method was. The original weight method (and the typical one in Schrofer’s applications) is based on a constant heartline drawn through a static array of nodes in the design space. The alternate method keeps the outside boundaries of the strokes constant, and shifts the locations of the nodes in the array to adjust weight. The nodes start from and move to different locations depending on whether the moving heartline runs from one outside node to another, or from an outside to an inside node or vice versa.