Add 6.09m to data values 1929-1936 to refer to RLR (1964)
Add 4.87m to data values 1937-1965 to refer to RLR (1964)
Add 4.85m to data values 1966-2007 to refer to RLR (1964)
Add 4.831m to data values for 2008 to refer to RLR (1964)
SUBTRACT 0.961m from data values 2009 onwards to refer to RLR (1964)
RLR (1964) is 10.5m below BM d
