Readability like adequate illumination is also important as a factor essential for efficiency in reading. A page which is not readable can obscure vision and produce visual discomfort and fatigue. Many factors are involved in determining the legibility of a printed page. These factors include the size of the type, the type face, the length of the printed line, the paper and the ink used in the printing of the page, the kind and size of illustrations and the presence or absence of decorations on the page margins. These aspects cover the external readability.