Add 4.945m to data values 1979-1997 to refer to RLR (1994)
Add 4.941m to data values for 1998 to refer to RLR (1994)
Add 4.945m to data values 1999 onwards to refer to RLR (1994)
RLR (1994) is 12.14m below Attached BM - Standard Mark
