An explanation is here (in interlingua).

Un explanation es hic.

# Pythagoras-style intervals (as separate prime factors in
# numerator and denominator) for 12 semitones in the octave.
#
# The program zarlino will then calculate the ratios for
# all combinations of pitches.
              1 : 1                 # unison, prime   1:1
2 2 2 2 2 2 2 2 : 3 3 3 3 3         # minor second  256:243
            3 3 : 2 2 2             # major second    9:8
      2 2 2 2 2 : 3 3 3             # minor third    32:27
        3 3 3 3 : 2 2 2 2 2 2       # major third    81:64
            2 2 : 3                 # fourth          4:3
    3 3 3 3 3 3 : 2 2 2 2 2 2 2 2 2 # augm. fourth  729:512
              3 : 2                 # fifth           3:2
  2 2 2 2 2 2 2 : 3 3 3 3           # minor sixth   128:81
          3 3 3 : 2 2 2 2           # major sixth    27:16
        2 2 2 2 : 3 3               # minor seventh  16:9
      3 3 3 3 3 : 2 2 2 2 2 2 2     # major seventh 243:128
#             2 : 1                 # octave          2:1