Solution to the King's problem with observables being not mutually complementary

We investigate the King's problem of the measurement of operators $\vec{n}_k \nobreak \cdot \nobreak \vec{\sigma} (k=1,2,3)$ instead of the three Cartesian components $\sigma_x$, $\sigma_y$ and $\sigma_z$ of the spin operator $\vec{\sigma}$. Here, $\vec{n}_k$ are three-dimensional real unit vectors. We show the condition over three vectors $\vec{n}_k$ to ascertain the result for measurement of any one of these operators.