Post Az7jsSfRT4D6OcFd68 by drj@typo.social
 (DIR) More posts by drj@typo.social
 (DIR) Post #Az7js3G3wI3RafBVZI by drj@typo.social
       2025-09-17T17:38:52Z
       
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       So if anyone wants to participate in a crowd-sourced effort to discover the pixel ratio of the ZX Spectrum, they could type this program into their Speccy and take a photo of the screen as square-on as you can get it; that would be great. Sample from emulator on right.#Retrocomputing #ZXSpeccy
       
 (DIR) Post #Az7js4leKKuoGuyFRQ by drj@typo.social
       2025-10-10T06:45:40Z
       
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       I would be very interested @Shaos in seeing the above grid (uptoot) on your 4MHz clone.
       
 (DIR) Post #Az7js5eF3MaH0EVqXA by Shaos@mastodon.social
       2025-10-10T07:01:44Z
       
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       @drj There is a problem with Ural-8/64K - its board based on Baltic schematics and it has bright signal somehow lost, so it is showing everything in "dark" mode:
       
 (DIR) Post #Az7js6l0vfayRWgljE by drj@typo.social
       2025-10-10T07:17:12Z
       
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       @Shaos the grid colour doesn't really matter for me. You could replace BRIGHT b with PAPER b*6
       
 (DIR) Post #Az7js7xSSt8yAPWDlQ by Shaos@mastodon.social
       2025-10-12T03:48:57Z
       
       0 likes, 1 repeats
       
       @drj Found it :)
       
 (DIR) Post #Az7jsBoO8YGW7RJ2BM by drj@typo.social
       2025-09-17T20:07:10Z
       
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       Here's mine. Holding the camera free on the left; on the right using my OrthoScope TM (a cardboard box with a small hole in it).
       
 (DIR) Post #Az7jsBtLq6EeMpczuy by Shaos@mastodon.social
       2025-10-10T07:02:07Z
       
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       @drj More info about Baltic in English: https://zxbyte.ru/baltic_en.htm
       
 (DIR) Post #Az7jsK0NfqbzWwyizA by drj@typo.social
       2025-09-17T20:28:02Z
       
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       So my calculation on the full checkerboard 2590/1689/(256/176) which is… 1.054. I also measured using a tape measure (quite hard as the true screen is many mm behind the front sheet of plastic): 522mm/335mm/(256/176) = 1.07.I also measured the "4:3" area on my TV: 688mm:513mm which is 4:3 * 1.0058 (so, correct up to my ability to measure it at this moment in time).Conclusion: Panasonic Viera displays 4:3 area correctly. Observed ZX Spectrum pixel aspect ratio very close to theoretical 1.055
       
 (DIR) Post #Az7jsScbdbwSFovMg4 by drj@typo.social
       2025-09-17T21:09:38Z
       
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       Using this observed ZX Spectrum pixel aspect ratio of 1.054 and knowledge that the pixel clock is 14 MHz to estimate the pixel clock of a true square pixel, gives a true square pixel clock estimate of 14.76MHz; absurdly close to the industry standard 14.75MHz and the true value of 14.77MHz. Haha.#Pixels
       
 (DIR) Post #Az7jsSfRT4D6OcFd68 by drj@typo.social
       2025-09-17T20:40:39Z
       
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       My theory for pixel aspect ratio is that there are 576 lines on a 4:3 display so horizontally there are 768 square pixels. Active image timing for PAL is 52µS (or maybe 51.95, who can say). So the ZX Spectrum with a 14MHz pixel clock has an aspect ratio of 768:52×14 which is 1.055 (minus rounding).