viewable image - technical definition

The actual diagonal image on a monitor screen. For a long time, CRT measurements have been overstated; for example, a 17" CRT is generally between 15" and 15.8" diagonal. On the other hand, flat panel monitors on laptops, and later on desktops, have always provided accurate measurements, which is known as "viewable image." A 15" flat panel is actually 15" diagonal. What a concept!