The above graph is fairly self explanatory. On the left hand side we have the primary vote levels for the two major parties, and on the right we have the minor + undecided vote level.The grey dashed lines are the general elections.
The horizontal dashed blue line represents 43% which is the rough primary vote level the Coalition needs to get more than for it to win an election. The horizontal dashed red line represents 40% which is the rough primary vote level the ALP needs to get more than for it to win an election.
Also marked on there are some things which have caused shocks to one or more of the groups primary vote series. The GST, the Ryan by-election, Workchoices and the Latham and Rudd leaderships.
There’s a lot of info contained in that graph, such as where the minor party and undecided vote goes when it contracts, which party is gaining support at the expense of which other party. It shows the difference between the spikes of the Rudd and Latham leaderships to name but a few.