Annotations can be used to indicate significant changes to your website that might effect your rankings in the Google search results. To add annotations, open one of the graphs, and then click on the date you wish to be associated with your annotation:

Or you could go to the Annotations-tab which can be accessed through the navigation window to the left.

All added annotations are available under the "Annotations"-tab and depending on when they were made they will also be visible on the graph in the Keywords-tab.

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