1. The problem statement, all variables and given/known data Find the eigenvalues and eigenstates of the spin operator S of an electron in the direction of a unit vector n; assume that n lies in the xz plane. 2. Relevant equations S|m>= h m|m> 3. The attempt at a solution This question is from Zettili QM and they have written: n.S|m>= (h/2) m|m> I do not understand why are they taking a half. If I take m=1/2 in S|m>= (h/2) m|m>, I get h/4 but the answer should be h/2, by using S|m>= h m|m>. So where am i going wrong?