Subtract 1.066m from data values 1938-1952 to refer to RLR<br>Subtract 1.089m from data values 1953-1959 to refer to RLR<br>Add 0.002m to data values 1960-1971 to refer to RLR<br>Add 3.763m to data values 1979 onwards to refer to RLR<br>RLR is 11.199m below primary benchmark SH 2553 8287