I'm reading Griffith's Introduction to Quantum Mechanics and came across the extract below:
"What if I made a second measurement, immediately after the first? Would I get C again, or does the act of measurement cough up some completely new number each time? On this question everyone is in agreement: A repeated measurement (on the same particle) must return the same value. Indeed, it would be tough to prove that the particle was really found at C in the first instance, if this could not be confirmed by immediate repetition of the measurement."
So the text implies that a second position measurement on a particle will return the same value as the first. However if position is known, then the momentum (and hence velocity) should be uncertain according to the uncertainty principle, and therefore shouldn't the position of the particle have changed between the first and second measurement (due the particle having an uncertain and likely non-zero velocity)?