Add 6.036m to data values up to 1964 to refer to RLR(1987)
Add 6.95m to data values 1965-1979 to refer to RLR(1987)
Add 5.73m to data values 1980 onwards to refer to RLR(1987)
RLR (1987) is 10.3m below TGBM HU 4783 4129
