Summary of Modern Quantum Mechanics
The Stern-Gerlach experiment
SG experiment measures the z-component of the magnetic momentum $\mu$ of random oriented silver atoms, which are expected to distribute continuously between $[ -|\mu|, |\mu| ]$, but are actually realized in the two quantized spots.
Furthermore, concating multiple SG apparatus show that determining x,z component simutaneously is impossible. Measuring one will destroy info of the other.
 Sakurai, Jun John, and Eugene D. Commins. “Modern quantum mechanics, revised edition.” (1995): 93-95.