“Rules of Quantum Mechanics (Part Two) There are certain observable quantities we can choose to measure, such as position, and when we do measure them, we obtain definite results. The probability of getting any one particular result can be calculated from the wave function. The wave function associates an amplitude with every possible measurement outcome; the probability for any outcome is the square of that amplitude. Upon measurement, the wave function collapses. However spread out it may have been pre-measurement, afterward it is concentrated on the result we obtained.”