wikipedia: http://en.wikipedia.org/wiki/Burn_down_chart

These things are useful.

The chart is generated automatically by some Agile project management tools.

You put in your UserStory and task estimates and enter your start and done dates.

You can see if you've more work coming in than going out and you can calculate actual hours vs estimates and gauge your estimation accuracy.

----

Sometimes the BurndownChart burns up.
See ErikTheVikingSyndrome

----