Add 5.281m to data values 1958-1972 to refer to RLR<br>Add 6.046m to data values for 1978 to refer to RLR<br>Add 6.059m to data values 1981-1997 to refer to RLR<br>Add 5.993m to data values 1998 onwards to refer to RLR<br>RLR is 10.700m below primary benchmark Trig