When the spin of this particle is measured with respect to a given axis (in this example, the x axis), the probability that its spin will be measured as ⁠ ħ / 2 ⁠ is just | ⟨ ⟨ ψ ψ x + | ψ ψ ⟩ ⟩ | 2 . Correspondingly, the probability that its spin will be measured as – ⁠ ħ / 2 ⁠ is just | ⟨ ⟨ ψ ψ x − − | ψ ψ ⟩ ⟩ | 2 . Following the measurement, the spin state of the particle collapses into the corresponding eigenstate. As a result, if the particle's spin along a given axis has been measured to have a given eigenvalue, all measurements will yield the same eigenvalue (since | ⟨ ⟨ ψ ψ x + | ψ ψ x + ⟩ ⟩ | 2 = 1 , etc.), provided that no measurements of the spin are made along other axes.