Instruct: Classify a review as either positive or negative.
Query: Explains a problem few know about today.

I did not even realize navigation was a problem in the time of Isaac Newton, or that longitude could not be accurately calculated. This was a fascinating look done in typical NOVA style into the problem, and how it was solved not by the great mathematicians and astronomers of the time, but by a watch maker. A nice video for those interested in science, navigation, or history.