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Re: Making pt a non-physical unit

From: Alan Gresley <alan@css-class.com>
Date: Mon, 11 Jan 2010 19:06:17 +1100
Message-ID: <4B4ADBF9.503@css-class.com>
To: Alex Mogilevsky <alexmog@microsoft.com>
CC: "L. David Baron" <dbaron@dbaron.org>, "robert@ocallahan.org" <robert@ocallahan.org>, www-style <www-style@w3.org>
Alex Mogilevsky wrote:
> Apparently the whole point of discussion is a concept of treatment of 'pt' that is different from other units when it relates to actual display resolution, and it is a kind of treatment that I was not aware of. I have been paying attention to this thread but I am still not sure what exactly is the relationship of 'pt', 'px' and 'in' are in Mozilla and what becomes problematic when dpi is different from 96.

Hello Alex, maybe this will help your understanding of the difference 
between 'pt' and 'px' with a different DPI setting.


'pt' are rendered larger when the DPI setting in increased or rendered 
smaller when the DPI setting is decreased.'px' stay the same.

In the days of the old west, you had monitors that show 72pt per inch 
(or 96px per inch) and if you were to get a ruler and measure this inch 
on a curved screen (with a flat ruler) then it would be about the same 
length. This is the legacy of old television screens, maths in early 
technology and binary code.


"A typical resolution of 720×480 and 720x576 means that the television 
display has 720 pixels across and 480 or 576 pixels on the vertical 
axis. The higher the resolution on a specified display the sharper the 

For 720x576 we can divide this by six to get 120x96 and this divided by 
six again gives us 20x16 with is a ratio of 5:4.

For 720x480 we can divide this by six to get 120x80 and this divided by 
five gives us 24x16 with is a ratio of 4:3.

Alan http://css-class.com/
Received on Monday, 11 January 2010 08:07:02 UTC

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