Typically monitors are advertised
by the diagonal size of the picture tube in inches. Common sizes
are 14", 15", 17", 20"+. However, the amount
of the screen that can be seen is usually less. For example,
most 17" monitors have only a 15.5" diagonal area
used for display, in part because the actual phosphor area is
only about 16" due to the glass thickness. This is partially
due to the fact that the monitor's case covers the edge of the
tube, and partially because monitor manufacturers want to make
you think you're getting a larger display than you are.
