This scale is used as the chord scale for the diminished seventh chord. Naturally, as the diminished seventh chord is symmetric and therefore, sounds the same when started from either note, the same goes for the scale. For example, this scale starting on C (C D E F G A B B()) can be applied to C7, which in turn is enharmonically equivalent to A7, F7 or E7. Note that the diminished chord is always tense and its seventh is double flattened (7); therefore, only in diminished context can a 6 (or 13) be played simultaneously with what is the enharmonic equivalent of a 6 (voiced only a major seventh above it or a minor second below it, the latter being only valid in piano voicings, but never a minor ninth below it). It is also the only context where the major seventh is considered a tension, rather than a chord tone. Similarly, only in Dorian/Mixolydian context can a 6 (or 13) be played simultaneously with what is the enharmonic equivalent of an augmented 6th (voiced only a major seventh above it or a minor second below it, the latter being only valid in piano voicings, but never a minor ninth below it). Also, only in Aeolian/Phrygian context can a 6 (or 13) be played simultaneously with the 5 (voiced only a major seventh above it or a minor second below it, the latter being only valid in piano voicings, but never a minor ninth below it).