The spacing is based on the font size and the track number. The user or application selects the font size and track number and the correct amount of interglyph space for each glyph in the font is calculated and applied to the text. The information you specify in the tracking table is used to calculate the proper amount of spacing for all glyph sizes of your font.
Tracking is similar to kerning .
Tracking controls the amount of spacing by performing a calculation that uses point size and a specified track number to determine interglyph spacing adjustment. The same adjustment is applied to all glyphs in the font. In contrast, kerning considers the identity of two or more neighboring glyphs to select pre-determined interglyph spacing adjustment values. The following figure shows how tracking makes adjustments to a glyph's advanced width to achieve tight, normal, and loose text, depending upon the track value. The amount of reduction or increase in the advanced width is determined by the use of per-size track values stored in the tracking table.