Add 4.814m to data values up to 1964 to refer to RLR (1971).
Add 4.21m to data values 1965-1979 to refer to RLR (1971).
Add 4.193m to data values 1980 onwards to refer to RLR (1971).
RLR (1971) is 10.2m below TGBM SU 6269 0053
