From sundials to atomic clocks, our understanding of time has become a lot more accurate as technological developments ...

Thanks to the Harrison's clock keeping exact Greenwich Mean Time, sailors could then determine how many hours they were before or after that time and thus able to determine their longitude ...

longitude, and elevation. We’ve far surpassed the Harrison H4, but clock accuracy has never been more important for finding our way.

But those alone won't let you calculate longitude - your position ... you're somewhere south-west of Moscow. What John Harrison did was to invent a clock, a chronometer, that would go on ...