'Diagram showing the Principal Triangulation for the Ordnance Trignometrical Survey of Great Britain and Ireland.' Outline map with trigonometrical points named. 1 inch to 24 miles.
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This is made available here purely for research purposes, and should not be duplicated or redistributed.
“Reproduced by kind permission of Ordnance Survey © Crown Copyright NC/2004/35281” from The National Archives File OS 5/27