It works even if the process is "we ask an oracle for a prediction". The more that Nate Silver produces new prior probability estimates for events, the better

It works even if the process is "we ask an oracle for a prediction". The more that Nate Silver produces new prior probability estimates for events, the better an idea we can get of the accuracy of his process. This measure is calibration, as the original article mentions. If our oracle tells us that an event has a 70% chance of happening, then regardless of whether the event happens or not we can't say much about the oracle's calibration. But if, out of 100 independent events the oracle has predicted to each have a 70% chance of happening, 69 of those events actually happened, then that tells us quite a bit.