Unit: metre
Data source: EPSG
Information source: Ordnance Survey of Great Britain.
Revision date: 2006-11-27
Remarks: Original definition is a=20923713, b=20853810 feet of 1796. 1/f is given to 7 decimal places. For the 1936 retriangulation OSGB defines the relationship of 10 feet of 1796 to the International metre through ([10^0.48401603]/10) exactly = 0.3048007491...