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We have no idea how it would even be possible to make these horizontal adjustments with the typing machines of the time.

I agree with the other comment here that the authors haven't used a typewriter, or at least in enough detail to know that on many if not all of them, holding down the spacebar will advance the carriage by half a character (and releasing it, in normal use, advances the other half.)

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Similarly the authors talk about how the multiline brackets were hand-drawn, and how could they be that precise? They might now know how common engineering stencils were for such things. Just find the bracket of the right size, and trace it onto the page.

I recognized the names of two of the authors immediately, David F. Brailsford, and Brian W. Kernighan. Not only are they both contemporaries of Ritchie, but Kernighan was a close colleague too.

Yeah, Kernighan is the K in K&R as in the other author of "The C Programming Language" as well as the "K" in awk, he's not just some dude speculating.

And the third one is his younger brother.

David Brailsford is an absolute gem, he speaks at length on Numberphile and Computerphile on YouTube: https://youtube.com/playlist?list=PLUTypj9XuPp4YBaHucPvr-zis...

He has a video about Dennis' thesis here: https://youtu.be/82TxNejKsng

IMHO, he's the David Attenborough of Computer History.

> the authors haven't used a typewriter

The authors are the famous Kernighan and Brailsford (!). They spent their life on stuff like this, and know him personally very well. They are talking about spacing much finer than half-character.

They are talking about spacing much finer than half-character.

Where? 1/24" is all they mention, which is half the normal 1/12" character spacing.

There's vertical spacing of 1/24″ in some places, which is twice the usual Selectric precision (6lpi with half-line motion). To me the most likely explanation is a Selectric variation with twice the detents, or even a third-party add-on, made specifically for technical reports.

It is too late for me to edit my other comment, but IBM offered ratchet wheels with double the normal number of teeth (54 rather than 27), providing quarter-line motion, for the Selectric.

p11 https://bitsavers.org/pdf/ibm/typewriter/selectric/PCE-008-1...

Ok that certainly seems to explain the vertical spacing.

Was there something that would allow for the the fancier horizontal resolution tricks?

Some other comments¹ have said that some Selectrics had a half-space control, so that would provide 1/24″ horizontally. I think that's the finest in the paper, unless I've missed a case.

¹ e.g. https://news.ycombinator.com/item?id=35177786

> holding down the spacebar will advance the carriage by half a character (and releasing it, in normal use, advances the other half.)

backspace did something similar, it was a common error correction to reposition the carriage halfway between two letters to sqeeze-in/add a letter that had been missed (once you get used to computers it's hard to remember that backspace didn't delete anything, it just moved you back)

>once you get used to computers it's hard to remember....

True, but there's a big clue in the name.

that clue could be interpreted as "type a space going backward, wiping out what was there" because 0x20 SPC is an ascii character which is a blank, while "space" on a typewriter is an abstract relative concept, depending entirely where you very finely (but very hard to see) positioned the carriage and it's not guaranteed to be blank if you position it where there is some preexisting typewritten ink.

Do the general populace understand a space on a word processor to be an ASCII (or utf) character though.

Further how would a backwards space work under that model? Wouldn't that jump back to the previous character? But it's not obvious to me that it would obliterate the previous character

yeah, i don't think the general populace understands, but I'm talking to nerds here who understand ascii and are fascinated by the history of word processing technology, as this entire topic is about :)

It moved you back, one space.

I'm talking about a mechanical typewriter, not an electric, what where you, rich? :)

backspace moved you back smoothly as you pressed harder and harder till you let go of it and it encountered the little ratchet thing and stuck there, one space back.

during the transition of smoothly moving back toward the ratchet, you could type another character anywhere on the way, and to catch the ratchet it actually had to move you back beyond one space.

...and then you had to use something like this https://en.wikipedia.org/wiki/Tipp-Ex to "delete" a mistyped letter by typing it again in white, and then correct the error.

The thesis has even finer horizontal spacing, creating a perfect centering effect of variable width line numbers, while the rest text on the same line is grid aligned. It's not something you do with a typewriter, unless you are a computer science PhD.

For the selectric typewriter, the horizontal spacing can be manipulated by swapping between different typewriter golf balls.

Pre-computer age summer high school project utilized different selectric golf ball fonts & spacing to make use of the golf font characteristics to create text pictures/art (font kerning & spacing). The high schoolers that participated in the project were not university admits yet.

The ultimate thesis hack, automated web page search & comparison to find selectric golf balls that match the thesis paper font/type/kerning.

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