Automatic kerning refers to the kerning applied automatically by a program, as opposed to no kerning at all, or the kerning applied manually by the user. There are two types of automatic kerning: "metric" and "optical". With metric kerning, the program directly uses the values found in the kerning tables included in the font file. Most systems with typographic features today provide this type of kerning. Optical kerning, on the other hand, is available only in the more advanced systems. With optical kerning, the program uses an algorithm to calculate, from their outlines, the optimal spacing for each pair of consecutive characters. With both types of automatic kerning, the system usually permits the user to specify a minimum font size for applying kerning, if the user feels that kerning is unnecessary for smaller font sizes.