Many traditional dance tunes retain the binary form of classical dance, following an "AABB" pattern of two distinct strains played twice each, the "A part" and "B part" typically being 8 measures (16 downbeats) in length, making one playing of the tune 32 measures (64 downbeats). In a few tunes the A and B parts are half the normal length; in others, particularly those derived from marches or rags, one or more parts are twice the normal length. Practice varies among fiddlers as to whether to repeat the parts of such non-standard tunes.