There are other plotters around that time, roland's for instance, that used a more obvious cartesian model. IE a 'print head' sliding on an x-axis rail, that sl

There are other plotters around that time, roland's for instance, that used a more obvious cartesian model. IE a 'print head' sliding on an x-axis rail, that slides on an y-axis rail. (https://www.youtube.com/watch?v=uECs0F8Txj0 https://www.youtube.com/watch?v=uECs0F8Txj0, the roland dxy-1200) Obviously if you use a roll of paper you need to run the paper itself back and forth unless you want to build something as big as a shopbot style table. I think the design for the 'roll-paper' plotters drove the design of much smaller plotters like the 7475a (which also moves the paper on one axis). Perhaps HP had a patent on that 'paper moves on one axis, pen moves on another? Regardless, both designs were present in the 80s.