Add 8.096m to data values up to 1994 to refer to RLR (1981)
Add 8.057m to data values for 1995 to refer to RLR (1981)
Add 8.034m to data values 1996-2002 to refer to RLR (1981)
Add 6.528m to data values 2003 onwards to refer to RLR (1981)
RLR (1981) is 8.8m below BM R 137
