Picture from "Feuerwerks und buchsenmeisterbuch"

[Matchlock]

Alright,

Now I went thru the book (ca. 1470, Cod germ. 734, Bavarian State Library Munich), only to find my surmise confirmed: there is no caption to the illustration nor is there a reference in the (very hard to read!) text.

However I found a similar but more exact line drawing in there (first attachment) and all of a sudden the idea of a primitive caliper rule jumped to my mind (a modern version also attached).

Any comments out there?

Best,
Michael