But how does one calculate longitude where there aren't helpful metal lines screwed into the ground? That was a question that puzzled some of the top minds for years, and after far too many ships were wrecked parliament passed the Longitude Act in 1714.
To commemorate its 300th anniversary there is currently an exhibition on the subject of Ships, Clocks & Stars: The Quest for Longitude at the National Maritime Museum (NMM).
Some of the suggestions put forward were simply bonkers - and in one case cruel to the dogs that were thought could have been used as a communications medium. More sensibly, John Harrison developed with his famous H4 watch that could be compared against local time to calculate longitude to sufficient accuracy.
All of Harrison's watches are part of this display - a remarkable collection.
Up on the hill above the NMM sits the Royal Observatory where official time was marked by dropping the red Time Ball every day at 13:00 precisely:
For example take these great quadrants that were used in calculating angles, such as this one used by Halley (which is actually just outside the exhibition but I didn't take a picture of the one inside):
Longitude Punk'd exhibition was built, in particular The Rime of the Ancient Commodore, which starts:
There was an ancient Commodore,
My Granddad told to me,
Who'd lived three hundred years before
And sailed a wond'rous sea,
With flocks (or herds) of Kiwi birds,
A wander was he
I found myself laughing out loud at this one, which was attached to a sad picture of a ship o' the line aground: