It was around 1/96" on a conventional PC screen because that was the conventional pixel density for PC screens; it was 1/72" (i.e. 1pt) on a conventional Mac screen for the same reason. That was something to deal with already in the GIFs-in-tables era and remained one as we moved on to CSS, right until Retina happened.

Unfortunately, Retina gave us a nonsensical and hacky “scaling ratio” rather than separate and independent units of physical length, viewing angle, and interaction granularity. (I still can’t get an A4 PDF in GNOME to display at “100%” such that it would actually be 210mm wide on my screen. And Darktable is the only piece of software I know where you can configure ppi and ppd separately.)