Term used by Messiaen in his Technique de mon langage musical (Paris, 1944; Eng. trans., 1956, chap.16) for a Scale which can be transposed by a semitone fewer than 11 times before the original set of notes reappears. Examples include the whole-tone scale (mode 1 in Messiaen's system, reproduced after two successive semitone transpositions) and the octatonic scale (mode 2, reproduced after three).