  Within quantum mechanics it is possible to assign a probability to the chance
that a measurement has been made at a specific time t. However, the
interpretation of such a probability is far from clear. We argue that a recent
measuring scheme of Rovelli's (quant-ph/9802020) yields probabilities which do
not correspond to the conventional probabilities usually assigned in quantum
mechanics. The same arguments also apply to attempts to use the probability
current to measure the time at which a particle arrives at a given location.
