# Quantum entanglement, quantum measurement, spin and position

By uncertainty principle, we know that determining particle's position at some location is limited. So we cannot determine the position of a particle at some exact point location as this would make the standard deviation of momentum reach infinite.

But as far as I know, spin is exactly determined when a particle gets measured - although before measurement it can exist in superposition of different states.

So, why are these two quantities(?) different? (Also, as far as I know, spin is part of wavefunction that includes position, right?)

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The uncertainty principle does apply to spin. For example we can measure the spin in the $z$ direction and the $x$ or $y$ directions, but we can't measure both $S_z$ and $S_x$ or $S_y$ at the same time because the operators don't commute. However we can measure total spin and $S_z$ (or $S_x$ or $S_y$) at the same time because the operators for total spin and spin in a particular direction do commute.