Two measurements describe the size of your display : the aspect ratio and the screen size. Historically, computer displays, like most television, have had an aspect ratio of 4:3 – the width of the screen to the height is four to three. For widescreen LCD displays, the aspect ratio is 16:9, very useful for viewing DVD movies, playing games and displaying multiple windows side by side. High definition TV also uses this format. The viewable screen size is measured diagonally, so a 19” screen measures 19” from the left to the bottom right.