A spin S particle goes through two successive Stern-Gerlach experiments, the second one with axe turned by an angle theta. Is it a formula giving the probability of measuring y in the second device knowing that x has been measured in the first? To be clear: for spin 1/2, we have the classical formulas:p(1/2|1/2)=cos²(theta/2) and p(-1/2|1/2)=sin²(theta/2). I've found formulas for S=1. I'm looking for a generalization for spin S. All I have found is that you have to use Clebsch-Gordan coefficients. Ok, I don't know how to do that. Please what is the formula? I guess it's a classical result.