Pixel to print ratio: 100 pixel/inch - 72% of print size.

Apple 30-Inch Cinema HD Display

In an article on Apple's cinema display, an obscure factoid. 100 pixels/inch is the standard for Apple displays. I think 72 pixels/inch gives fonts that are the same size as printed fonts, so 100 pixels per inch means ...

: ... One final note about resolution. All monitors are, of course, different in terms of the ratio between resolution and screen real estate. The Apple 30-inch Cinema HD Display, at its optimal resolution, displays images at a pixel density of 100 pixels per inch, which means that the things on your screen will be about 72 percent the size they would be if you were to print them out at 100 percent. Personally, I'm used to this, as my 22-inch widescreen CRT does the same thing. But it can make small text a bit difficult to read, particularly serif text below about 9.5 points. But you can always crank the resolution down for a larger image, or up the magnification of your documents for easier viewing.

It's interesting that most discussions of displays omit the pixels/inch number -- but it's the most interesting number for me.

Of course a scalable interface would allow this sizing ratio to be adjusted. I believe that a long forgotten Commodore/DOS OS did this in the 1980s (I can't even recall the name myself any more!).