Hi, I have one of those, can't find it now in my sewing room! But, the numbers don't really mean anything, I think they go from 1 to 24. They are just to help you identify which color you were looking at.
If you want to identify the complementary color to your color, you can add 12 to its number to find the complement. However, that's not necessary since the tool also lists the complements,triadic colors and other color harmonies for each color on the card for that color.
The colors make a color wheel with 24 steps. You can fan the cards out to make a circle and see the steps.
No magic really, just a convenient way to keep track of the colors.
Kathy