By looking at the Sprint Burndown chart, when do you think that the stories are moving as per the schedule code example

Example: what is burndown chart

A burndown chart is a graphic of how quickly
the team is working on user stories. Basically
it shows the total done work against
the amount of total work. One of the benefit of
burndown chart is that it provides an updated
status report on the progress of the project. 
We use JiraXray to track burndown chart.