Actual Sydney Surf from MHL

If you surf in Sydney you must know about the waverider buoy that is read by Manly Hydraulics Laboratory (MHL). Here (and on RealSurf.com) is the link to each day's data which includes the previous three days'' data:
mhl.nsw.gov.au/data/syddir.gif
At first sight the plot does not look easy but with a little study it ends up being both simple and incredibly useful.
Click the graphic for the clues to the information, but note the graphic is for the date 20 November 2011.
Compare that date with the current graphic.