This was the device used for quality printing in the 1970s. It looks like a typewriter (and could be used as one), but in reality it was a powerful computer terminal, capable of responding to all sorts of host-generated commands. To illustrate, the SCRIBE document preparation system was capable of producing output for the Diablo, which, when passed through a locally written spooler program (on the DEC-20), could move the paper up and down in precise increments and even handle the mounting of different print wheels on the fly; for example the regular ASCII wheel and a technical wheel with math symbols, allowing the printing of complex mathematical expressions, e.g. big integral or summation signs, tall parentheses, etc, accomplished not only with the different print wheels, but also precise host-controlled positioning of the paper and print head, in what was considered publication quality. As I recall the spooler printed each page that required two print wheels in just two passes, the first for ASCII and the second for symbols, "rewinding" the page after the first pass. The CUCCA nuwsletter was printed on the Diablo for about 10 years, until laser printers came along. Quite a few PhD theses were printed on the Diablo too.
Trivia: Scribe files destined for Diablo printing were given the “.POD extension, for Prince Of Darkness.