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How are sea levels measured over time?
Chris Daniel, Colwyn Bay, Conwy, UK
Sea level has only been measured accurately since the early 1800s, when the US first began to systematically survey its coastline. This was originally done with a simple measuring stick to gauge the height of the water relative to a benchmark on land.
The stick was often used in a stilling well, a tube with a small hole placed below the water’s surface that dampens movement caused by waves. This surprisingly accurate system remained unchanged in principle – apart from the introduction of automated recording – until…
