I think he just used a common all-mechanical typewriter. Every typewriter I used as a kid had a fractional form-feed of at least two steps (half a line), and so

I think he just used a common all-mechanical typewriter. Every typewriter I used as a kid had a fractional form-feed of at least two steps (half a line), and some of them had horizontal rulers and even tabs on the carriage so you could accurately return it to any position you wanted. I loved drawing things with them by just moving the carriage around and re-aiming the typing aperture.