Each graph displays benchmark results relative to its baseline commit, which is usually the latest stable release at the time of testing. The 95% confidence interval is displayed in light gray. On hover, the graph displays the benchmarked commit at that point (click to view full commit).
Note that some commits are not tested, so there could be multiple commits (not shown) between two points on the graph.
Using the 'unit' search box above leads to a page that shows much more detail about each individual point in the selected time range. Another way of reaching this page is to click the unit name that acts as each graph's title, i.e. "sec/op".