If you don't want to subscribe to this newsletter to read about this program, https://archive.org/details/analog-computing-magazine-41/pag... is a link to the original article. And here's a video of it in action: https://www.youtube.com/watch?v=1glIV5yulw8
Finding letters regarding it in subsequent issues, is left as an exercise for someone else. :)
This article has now made me intensely envious of the Atari users who got actual assembly code source along with their long strings of hexadecimal type-ins, us c64 kids just got pages and pages of incomprehensible hex in everything except for Transactor.