All odd sizes are integers (37, 39, 41 etc.). Beginning with the odd sizes, increments of 2/3 are added to get to the next size:
37 + 2/3 = 37 2/3
37 2/3 + 2/3 = 38 1/3
The reason for the 2/3 size interval is this: Research has shown that most people do not need a difference of an entire size, but a 2/3 difference. For instance, I normally wear size 39. A kyBoot of this size is too loose, however. So I can wear size 38 1/3, which fits perfectly (size 38 would be too small).
Of course, there are customers who cannot find the perfect size even with the 2/3 intervals. The solution for these people is to take the next larger size and add a kybun filler sole to the shoe. This compensates for the extra space.