Since the CRT is encased in a plastic housing, also called a bezel, the viewable area of a monitor is always less than the stated monitor size. The viewable area is then the diagonal measurement of the portion of the CRT that is visible. Typically, the viewable area of a monitor will be about one inch smaller than the stated CRT size. Pixels or picture elements are the number of dots on the screen and are composed of one red, green and blue glowing phosphor dot. The more dots, the sharper the image.
Dot pitch refers to the distance between two same-colored red, green or blue phosphor screen dots.
Typical dot pitches range in distance from .25 to .39 millimeters. A smaller DPI indicates that more pixels are present in a measure of screen space and this yields a sharper screen image. Shadow-mask monitors are sometimes called dot trio monitors because their design uses phosphor dots arranged in red, green and blue triangles. The shadow-mask name derives from the phosphor dots being separated by a metal mask. Aperture-grille monitors, such as Sony Trinitron and Mitsubishi Diamondtron, use a phosphor coating of alternating red, green and blue vertical stripes instead of triangle dots.