[emeritus]

When using drawing ink on tracing paper or cloth, it is possible to make corrections such as removing ends of lines which have over-run, or even complete lines, by carefully scraping away the excess with a scalpel blade, preferably a rounded one like a Swann-Morton No. 10. That technique could have been used to create smooth transitions. The drawings would no doubt have been made on an enlarged scale and reduced for publication, which would have made any corrections and amendments easier to make and less visible in the final publication.