Hypercharge was a concept developed in the 1960s, to organize groups of particles in the " particle zoo " and to develop ad hoc conservation laws based on their observed transformations. With the advent of the quark model, it is now obvious that strong hypercharge, Y, is the following combination of the numbers of up (n u), down (n d), strange (n s), charm (n c), top (n t) and bottom (n b):