We review non-classicality of quantum datum. We consider whether we can assign the predetermined ^^ ^^ hidden'' result to numbers 1 and $-1$ as in results of measurements in a thought experiment. We assume the number of measurements is two. If we detect $|\uparrow\rangle$ as 1 and detect $|\downarrow\rangle$ as $-1$, then we can derive the Kochen-Speker theorem. The same situation occurs when we use a finite-precision measurement theory that the results of measurements are either $1-\epsilon$ or $-1+\epsilon$.