A pop history account of the competition between John Harrison, who made the first precision marine clock in around 1735, and the astronomers of the time (such as Edmund Halley, who figured out you could determine longitude by the difference between local time and time in some known place in Europe by published tables of when the moons of Jupiter would be eclipsed by Jupiter, or where the moon was in relation to the sun at certain predictable times once the orbits were worked out). Super interesting on the basics of measurement of something incredibly useful.