Leading: “The optimal line length for reading depends on two factors, a physiological factor, and a typographic one. The eyes can easily scan a width of about 6 inches at about a foot and a half distance, without the head moving. If the width is greater than this the head starts to move while scanning the line and this slows down reading. The eye must also return to the beginning of the next line, and with long lines of text this becomes more difficult, and we may start to skip a line, or read the same line again. To prevent this it is absolutely essential that long lines of text be given an increased leading. This factor is one of the main reasons [1] why reading on the computer screen is about 30% slower than reading the printed page.”