A Stern-Gerlach experiment can not only see the two distinct angular moment states of a spin 1/2 particle, but it can also select one of those states by filtering the particles going to one of the two "spots." These particles may then be analyzed by a second Stern-Gerlach appratus. If we prepare particles with spin in the z-direction in the first Stern-Gerlach apparatus measure the particles in the z-direction in the second apparatus, we will get all particles having spin in the (+) z-direction. On the other hand, if we prepare particles in the x-direction and measure them in the z-direction, we will get half the particles having spin the +z direction and the other half having spin in the -z direction. In the general case the fraction with spin in the +z and -z directions is determined by the expectation value of S_z for the incoming particles.