There is also this thing in Phoenix:
But back to the blog post. In my eternal quest for full typewriter justification, I found this little snippet:
The way that the attachment works is a mystery. From the description is seems that you note the number of spaces that remain on the line after typing. Some sort of pointer and ruler help you do this. In retyping, a knob s allows you to set the number of spaces to drop into the line to fully justify it. Maybe its something that fiddles with the spacer mechanism. The possibilities are very interesting. Maybe this is something that can be replicated if I channel my inner Thomas Edison.