The Cornish hut that gave rise to sea level bench mark

I had not realised such things were so relatively recent.

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I wonder if it sees any change to height over the years?

The tidal measurements that started in 1915 were to establish a vertical datum for Great Britain. There is tidal data for the UK that goes back to 1764.

This is the paper that the BBC News item is based on:

A Century of Sea Level Measurements at Newlyn, Southwest England

An exercise of ‘data archaeology’ of high water tidal information from Liverpool, NW England has resulted in the construction of a time series of ‘Adjusted Mean High Water’ spanning 1768 to the present which can be employed as a record of proxy Mean Sea Level (MSL). The time series, although gappy, is arguably the second oldest sea level‐related record in the world, after Amsterdam’s (1682, although the data we hold are from 1700 only) and of comparable age to Stockholm’s (1774).

From here:
High waters at Liverpool since 1768: the UK’s longest sea level record

Good article about vertical datums used in the U.S.

https://source.asce.org/getting-the-height-right-the-north-american-vertical-datum-of-1988/


Surveyors use a Fischer level at Glen Canyon in 1921. (NOAA)

In 19th century America, the expansion of the railroad famously led to the creation of our modern time zones, imposing temporal order on a nation that to that point set time by dozens of local “high noons.” In bridging east and west and transforming America into a continental nation, the railroads also shaped the development of geodetic surveying. In the late 19th century and through the early decades of the 20th, multiple vertical datums — the standard for accurate measurement of elevation across large distances — existed across the country.

The USGS topo map I have here of the local area uses NGVD of 1929. The more recent one uses 1988.

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arent there 3 datums to cover the GOM, the article doesnt seem to cover that.
Most large continents have several datums.