The horizontal axis represents time; each tick mark represents the first of a month. The last tick mark is the start of this month. Big ticks are the start of January.
The yellow bands represent weeks. The bar chart represents relative activity in each week, measured as number of checkins during the 7 day period from Monday to Sunday corresponding to that week band.
The vertical axis represents e-mails for the teal line, issue notes in the spec for the green line, and bugs for the navy line. Each tick mark represents 100 e-mails, issues, or bugs.
Raw data: issues count, revision activity.