In the TV series, Person of Interest, Harold Finch claims that, at one point, most of the Machine's memories were erased at midnight in order to keep it from becoming too powerful.
If that's the case, how did it correlate information over time in order to identify numbers? Also, why didn't it just forget about all the training that it did with Harold, forcing him to start over training it every day?
For example, a key piece of information in figuring out that a corrupt FBI agent was planning to sell plutonium was the fact that he kept going to the same gas station (even if he didn't need gas). How would the Machine know that if its memories were being erased?