Abbreviation for quindicesima or "at the fifteenth below." This indication is found below specific notes on a staff and indicates that those notes should be performed two octaves lower than written. This indication can be used with a dotted line that covers a series of notes to be performed at the fifteenth. The dotted line should end with a upstroke to indicate the end of the passage to be altered. The end of the passage can also be indicated by the term loco ("at place") or perform at the written pitch.
This indication is rarely used because of the difficuly that performers generally have in transposing two octaves lower.
It should also be noted that since an octave is eight notes and two octaves, being twice the interval, should be 16 notes After careful examination, it becomes clear that the last note of the first octave is the same as the first note in the second octave so there are only 15 notes in a two octave interval .