Add 5.717m to data  values 1957-1972 to refer to RLR(1964)
Add 6.191m to data values 1973-1978 to refer to RLR(1964)
Add 5.946m to data values 1979-1997 to refer to RLR(1964)
Add 5.843m to data values 1998-2002 to refer to RLR(1964)
Add 6.003m to data values 2003 onwards to refer to RLR (1964)
RLR (1964) is 9.6m below BM Z Z Z
LLD = Land Levelling Datum
