Add 3.746m to data values 1980-1981 to refer to RLR<br>Add 3.575m to data values 1982-1984 to refer to RLR<br>Add 4.575m to data values 1985-1987 to refer to RLR<br>Add 4.810m to data values 1988 onwards to refer to RLR<br>RLR is 10.500m below primary benchmark TM 3001 3414