[2] Inside the building is an Ordnance Survey benchmark, constituted of a brass bolt (OSBM SW 4676 2855), and a 1.6-metre (5 ft 3 in) diameter stilling well set into the pier which has ocean access via an inlet.

[3][4][5] The Ordnance Survey established the observatory in 1915 to contribute to the measurement of a national vertical datum defined by mean sea level.

Due to the stable underlying granite bedrock, the proximity to the open ocean, and the absence of rivers, the observations at Newlyn were selected as the basis, or ordnance datum, for elevation measurements across Great Britain.

To realise the reference datum across the country, in the early twentieth century spirit levelling techniques were used to measure a national network of circa 200 fundamental benchmarks, all referenced to the Newlyn brass bolt.

[1][3] The 6 years of observations captured at the observatory up to 1921 continue to define the height reference system for Great Britain, with varied applications including flood planning, understanding air pollution, infrastructure design, and deliveries by unmanned aerial vehicles.