Contexts of type 2 (“Measurement  Contexts”):[9] Carrying out a “measurement” of an observable \(B\) on a system in a state \(\ket{A}\) has the effect of collapsing the system into a \(B\)-eigenstate corresponding to the eigenvalue observed. This is known as the Collapse Postulate. Which particular \(B\)-eigenstate it collapses into is a matter of probability, and the probabilities are given by a rule known as Born’s Rule: