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This map shows the position of OS Benchmarks.
Benchmark data was taken from records obtained from Ordnance Survey here (the list is no longer maintained).
The list of Fundamental Benchmarks was obtained from bench-marks.org

Benchmark Display
Benchmarks are only shown at the appropriate zoom level (see 'more info')
Colour-coded markers show their location.
Clicking a marker shows the full benchmark information as downloaded from Ordnance Survey.

Pointer Locations
Locations used are the OS National Grid reference in the source data. The marker point indicates the south-west corner of a 10m square where the benchmark should be found.

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Benchmark Key
Cut Mark (the most common type)
Rivet (brass rivet on level surface)
Pivot (a hole on a level surface)
Bolt (PA Bolt/Stud Bolt)
Flush Bracket (numbered wall insert)
Bracket
Brass rod
Fundamental Benchmark

Flush Brackets with a star indicate a bracket at a Trig Point.

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Fundamental Benchmarks are the basis of the OS levelling system and the only ones still maintained by the Ordnance Survey.