There are a total of 16 classes, ranging from three moves with one center to nine moves with four centers, but only classes in which the ratio of centering moves to total moves is 1:6 or greater contain an aesthetic knot, eliminating three classes (ten knots) for a remaining 13 classes, with 75 knots. (In the "Nature" paper, the lower bound was placed at a more restrictive 1:4, eliminating the knot classes containing the Kelvin, Victoria, and Grantchester; this was likely revised specifically in order to include the Victoria/Prince Albert, which has fairly extensive historical documentation.) The most representative knot in each remaining class was then selected on the basis of symmetry and balance.