Add 5.491m to data values 1958-1972 to refer to RLR (1964)
Add 5.983m to data values 1973-1978 to refer to RLR (1964)
Add 5.844m to data values 1979-1997 to refer to RLR (1964)
Add 5.581m to data values 1998-2002 to refer to RLR (1964)
Add 5.811m to data values 2003 onwards to refer to RLR (1964)
RLR (1964) is 10.646m below BM HO 2
LLD = Land Levelling Datum
