It only just dawned on me lately that the resolutions for High Definition TV have a close connection with dozenals. The major resolutions are 720dpi and 1080dpi. Of course that is 60 x 12 and 90 x 12 respectively. Now does anybody have any input as to why these figures were adopted?

That would be a very high resolution for a television set. It's just 1080 pixels, not 1080 per inch.

Haven't been able to find why 1080 was chosen. Best suggestion I've seen is for backwards compatibility with older 540-pixel displays, but NTSC has only 486 scanlines, not 540.

Maybe something to do with monitors using 72dpi?

That would make sense: 720 px = 10 in, 1080 px = 15 in.

Also, it's common for monitors to have heights that are multiples of 60 px because the standard aspect ratio used to be 4:3 and the widths the monitors were multiples of 80 px (640 px, 800 px, etc.). Because text mode displays were 80 characters wide. Because IBM wanted compatibility with 80-column punch cards.

Geez, I am getting old! I should have worked that one out myself. My first job in IT was with IBM Canada in Toronto in 1963 and the input media then was the 80 column punch card. I knew the text screen was 80 characters wide for that same reason. It would make sense that things built on that format since it would have been easier to scale up from the existing character graphics by going in multiples of what already was to hand.

I still have an old IBM print ruler somewhere . That had 10 characters per inch which was the spacing of characters on an IBM 1403 band printer. Then there is something in the back of my mind that said 72 characters was the recommened maximum for printed reports.

And yes Dan, that 1080 dpi was a slip of the finger when the brain didn't keep pace.