The charge operator can be expressed in terms of the projection of isospin T 3 and hypercharge, Y : Q = 1 2 Y + T 3 , T 3 = T , T − − 1 , . . . , − − T . This is known as the Gell-Mann-Nishijima formula. The hypercharge is the center of splitting for the isospin multiplet: 1 2 Y = 1 2 ( Q min + Q max ) . This relation has an analog in the weak interaction where T is the weak isospin.