These Sea Level Pressure (SLP) measurements at Darwin was provided to us by Julie Cole (now located at?). It covered the period from Jan of 1882 through early 1991. I located a source for continuing updated information at the CAC climate bulletin:
nic.fb4.noaa.gov:pub/cac/cddb/indices
The climate bulletin runs from 1951 through the present and its contents are identical with the period Jan 1951 through early 1991 provided by Julie. The source of the earlier segment of the record are not known to me.
This is an important index for measuring ENSO.
The values are in millibars over the value of 1000 (i.e. a SLP measurement of 1107 is shown as 107).