Bench Mark :: Shared Description

Bench marks LinkExternal link were historically used to record the height above sea level of a location as surveyed against the Mean Sea Level data (taken at Clarendon Dock, Belfast, for Northern Ireland data, Newlyn in Cornwall for data in Great Britain and Portmoor Pier, Malin Head, for data relating to the Republic of Ireland). They were used as part of a greater surveying network by the UK Ordnance Survey, Ordnance Survey Northern Ireland (OSNI) and the Ordnance Survey Ireland (OSI). If the exact height of one bench mark is known then the exact height of the next can be found by measuring the difference in heights, through a process of spirit levelling. In this way hundreds of thousands of bench marks were sited all around the UK & Ireland from the mid 19th to late 20th centuries. There are several distinct types of bench mark:

- Fundamental bench marks have been constructed at selected sites where foundations can be set on stable strata such as bedrock. Each FBM consists of a buried chamber with a brass bolt set in the top of a granite pillar. See NG8825 : Dornie fundamental bench mark for an example. FBMs were used in Ireland as well as GB but those in Ireland do not have any surface markers, nor are they marked on standard maps.
- Flush brackets consist of metal plates about 90 mm wide and 175 mm long. Each bracket has a unique serial number. They are most commonly found on most Triangulation Pillars, some churches or on other important civic buildings. See J3270 : Flush Bracket, Belfast for an example.
- Cut bench marks are the commonest form of mark. They consist of a horizontal bar cut into a wall or brickwork and are found just about anywhere. A broad arrow is cut immediately below the centre of the horizontal bar. See J3372 : Bench Mark, Belfast for an example. The horizontal mark may be replaced by or contain a bolt - see J1486 : Bench Mark, Antrim.
Other marks include:
- Projecting bench marks such as SD8072 : Projecting Bracket Benchmark on St Oswald's Tower
- Bolt bench marks such as SJ1888 : OSBM bolt on Hilbre Island
- Rivet bench marks such as J3978 : Bench Mark, Holywood
- Pivot bench marks such as SJ2661 : Pivot bench mark on Leeswood Bridge

Bench marks are commonly found on older buildings or other semi-permanent features such as stone bridges or walls. Due to updated mapping techniques and technological advances such as GPS, bench marks are no longer maintained. Many are still in existence and the markers will probably remain until they are eventually destroyed by redevelopment or erosion.
by Rossographer
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4013 images use this description. Preview sample shown below:

SK5539 : Bench mark, Leen bridge, Triumph Road by Alan Murray-Rust
NO6107 : OS benchmark - Crail, 31 Castle Street by Richard Law
J5767 : Flush Bracket, Greyabbey by Rossographer
D3115 : Flush Bracket, Glenarm by Rossographer
SO7192 : OS benchmark - Bridgnorth, St Mary Magdalene Church by Richard Law
SK9303 : Bench mark, 6 Digby Drive, North Luffenham by Alan Murray-Rust
SD7306 : Bench mark, Cobden Mill  by Alan Murray-Rust
SK6730 : Bench mark, St Luke's Church, Kinoulton by Alan Murray-Rust
SJ8808 : OS benchmark - Brewood, cottage on Bargate St by Richard Law
SK5336 : Bench mark, #2a, The City, Beeston by Alan Murray-Rust
J3574 : Bench Mark, Belfast by Rossographer
SO7483 : OS benchmark - Highley, St Mary's church tower by Richard Law
SK3447 : Bench mark, 32 Green Lane by Alan Murray-Rust
SJ2188 : Corner of The King's Gap and Valentia Road, Hoylake by John S Turner
TQ3004 : Benchmark, Ship Street by Keith Edkins
SO9298 : OS benchmark - Lower Horseley Field, bridge by Richard Law
SK7039 : Bench mark and bolt, St Mary's Church, Bingham by Alan Murray-Rust
SO6287 : OS benchmark - Cleobury North, Glebe Farm by Richard Law
NO3501 : OS flush bracket S3153 on Duniface Hill trig by Richard Law
NY3239 : Benchmark, The Old Smithy, Caldbeck by Adrian Taylor
SD5631 : OS benchmark - Brookfield, St Mary Magdalene church by Richard Law
SK6211 : OS benchmark - Syston, High St railway bridge by Richard Law
SJ5015 : OS benchmark - Shrewsbury, no 25 Lancaster Road by Richard Law
SK7054 : Bench mark, 54 King Street, Southwell by Alan Murray-Rust
SJ8908 : OS benchmark - Somerford, cottage at track junction by Richard Law

... and 3988 more images.

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Created: Tue, 2 Mar 2010, Updated: Tue, 21 Feb 2023

The 'Shared Description' text on this page is Copyright 2010 Rossographer, however it is specifically licensed so that contributors can reuse it on their own images without restriction.

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