What is Reddit's opinion of Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time?

From 3.5 billion Reddit comments

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You may be confusing issues. (latitude, altitude, longitude)

Sailors wanted an accurate way to know the "time at port" to compare against local time (observable via stars or sun) so that they could compute their longitude (east or west location on the globe). (The difference in minutes would be equivalent to the relative difference in minutes of arc east/west.) Grandfather clocks (eg, pendulum clocks) wouldn't work for this, because the rocking of the ship would throw off the pendulum timing.

If I recall from the documentary based on Dava Sobel's book Longitude(Amazon) (looks like the documentary is available on youtube), the guy (John Harrison in 18th century) who rose to the challenge to make a clock that worked at sea had all sorts of problems with the pendulum motion, and somehow miraculously actually made a "pocket watch" to solve the problem.