Comment by pavlov
13 days ago
For CRTs, the diagonal measurement was of the physical tube. The actual viewable area was smaller. Part of the tube’s edges were covered by plastic, and there was always also some margin that wasn’t used for picture so it was just black.
It was a 9” tube with 3:2 aspect ratio. Your calculation of a 8.5” image at 72 dpi sounds right.
>For CRTs, the diagonal measurement was of the physical tube. The actual viewable area was smaller.
That's also why TVs and monitors of that era always seemed smaller than advertised. I remember having to explain that to a lot of people.