Chiseled into the walls of buildings around the UK are marks which might seem strange—even mysterious—if you’re not familiar with their purpose.
The symbols comprise a horizontal line with three lines pointing toward it to create an arrow. Although to the untrained eye they look more like indicators of a secret society, these marks—or benchmarks—played a vital role in mapping the United Kingdom for centuries.
Geospatial engineering and topographic surveys have traditionally used Ordnance Survey benchmarks (BMs) as reference points for establishing ground heights. There are three classes ofthese; first-order marks of high accuracy, usually anchored to solid rock and securely protected (fundamental benchmarks: FBMs), second-order marks established on stable structures and the more familiar third-order marks cut into walls and houses.
In the past Ordnance Survey maintained a dense network of these, ensuring that there would be one per square km in rural areas, denser in built-up areas. The BM network of some 500,000 BMs (generally 1912–56) was regularly checked and maintained. In 1972, however, Ordnance Survey effectively abandoned the network as too expensive to maintain and the BMs have been steadily disappearing and becoming increasingly less reliable ever since. There has been no resurvey since the mid-1980s.
Most town and city centres have an abundance of benchmarks. There’s at least 40 throughout Newcastle with quite a few of them located in the city centre. Walking along the Quayside you can find quite a few without having to even venture up into the centre… if you know where to look.
Front of Newcastle Guildhall, with OS Benchmark to right of door just above the pavement.
Guild Hall benchmark up close.
Benchmark on the corner of what is now the Premier Inn, facing out onto the River Tyne.
Benchmark concealed behind a drain pipe on The Waterline bar, which was once the location of a prominent waterfront warehouse.
James, H (1873). Account of the field surveying and the preparation of the manuscript plans of the Ordnance Survey. London: HMSO. (Scanned by National Library of Scotland).
 ‘Ordnance Survey Benchmarks: Their very limited use for civil engineering survey work’, Institution of Civil Engineers Briefing Sheet: 1.