This is only tangentially related, but Musical Set Theory uses from 0-11 to describe the 12 individual semitones of standard western harmony. I've always run under the assumption that they use that system because it makes the math easier when you start to deal with symmetrical intervals (Unison and an octave being the same, 4ths and 5ths being the same). Because the symmetrical intervals are treated the same, but you are often looking for the smallest possible intervals, you can find the smaller interval by removing the interval you have from 9 in Standard harmony, and 12 in Set theory. In traditional music theory, this means P4=P5, Maj3 =Min6, Min3 = Maj6. In Set theory this means that everything mirrors in 0-6, so 0=12, 1=11,2=10 etc. up to 6=6, the mirroring at the tritone. If you tried to start it on 1 instead of 0, that mirroring doesn't work out. 1=13,2=12, 3=10, 4=9, 5=8, 6=7? Oops. Just more proof that starting with 0 is easier, i guess.