Add 5.814m to data values 1962 to1977 to refer to RLR (1974)
Add 6.277m to data values 1978 to 1986 to refer to RLR (1974)
Add 5.814m to data values 1987 onwards to refer to RLR (1974)
RLR (1974) is 8.414m below BM 5371 A 1977
