This system is very economical, but is necessarily limited. For example, many of the classes may be quite small. Also, a font with many types of glyphs may require several such tables. Finally, many pairs remain that cannot be represented through classes. For them, simpler, one-dimensional tables are provided: each table is for a particular character that is the first in many pairs, and the entries contain the characters that are the second in these pairs, together with the corresponding kerning values.