Display size

The size of a screen is usually described by the length of its diagonal, which is the distance between opposite corners, typically measured in inches.

[1][2] The method of measuring screen size by its diagonal was inherited from the first generation of CRT televisions, which had picture tubes with circular faces.

Since these circular tubes displayed rectangular images, the diagonal measurement of the visible rectangle was smaller than the diameter of the tube due to the thickness of the glass surrounding the phosphor screen, which was hidden from the viewer by the casing and bezel.

It had the advantage of being a single number specifying the size and was not confusing when the aspect ratio was universally 4:3.

For full HDTV resolution, this one minute of arc implies that the TV watcher should sit 3.2 times the height of the screen away (optimal viewing distance).

Ideally, the TV watcher sits far enough away from the screen that the individual lines merge into one solid image.

The watcher may sit even farther away and still see a good picture, but it will occupy a smaller portion of their visual field.