Shared description

Bench Mark

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 Due to updated mapping techniques and technological advances such as GPS, bench marks are no longer maintained.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

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


3838 images use this description. Preview sample shown below:

SP1685 : OS benchmark - Marston Green, no 10 Holly Lane by Richard Law
D2327 : Bench Mark, Cushendall by Rossographer
SO9596 : OS benchmark - Bilston, Mount Pleasant by Richard Law
J3366 : Flush Bracket, Ballycowan Triangulation Pillar by Rossographer
SP0288 : OS benchmark - Smethwick, Holy Trinity church by Richard Law
SD6669 : Benchmark, Butterbur Cottage by Adrian Taylor
SJ4911 : OS benchmark, Belle Vue Tavern by Richard Law
J4844 : Flush Bracket, Downpatrick by Rossographer
SJ4905 : OS benchmark - Condover, roadside wall by Richard Law
SK6586 : Bench mark, Blacksmith's Lane corner, Torworth by Alan Murray-Rust
SJ1225 : OS benchmark - Llanrhaeadr-ym-Mochnant, former school by Richard Law
SJ8104 : OS benchmark - Albrighton, wall on Station Road by Richard Law
SK6989 : Bench mark, All Saints' Church, Mattersey by Alan Murray-Rust
SP1580 : OS benchmark - Lode Heath, 45 Cornyx Lane by Richard Law
C6809 : Flush Bracket, Dungiven by Rossographer
SJ8102 : OS benchmark - Boningale, Parkside Farm by Richard Law
J3373 : Bench Mark, Belfast by Rossographer
SU6687 : Bench mark and bolt, Holy Trinity Church, Nuffield by Alan Murray-Rust
SP1581 : OS benchmark - Elmdon Heath, electrical building by Richard Law
SD8913 : Benchmark, Rochdale, Midland Bank by Adrian Taylor
SE3259 : OS benchmark - Scotton, St Thomas' church by Richard Law
D0518 : Flush Bracket near Cloughmills by Rossographer
SO6293 : OS benchmark - Monkhopton, roadside building by Richard Law
SJ9315 : OS benchmark - Teddesley Hay, bridge 89 by Richard Law
SO7193 : OS benchmark - Bridgnorth, depot behind Mill Street by Richard Law

... and 3813 more images.

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