The Registration Chart shows the number of active registrations)  from the time of the first one.  

As a chart - you can see when the growth spurts are - and correlate them to your marketing activities to see what was more effective.

You can use the Setting Widget to customize the chart. Displaying by:

• Registrant Type: Attendee or Entity
• Chart Type: Interval or Cumulative
• Chart Interval: By Day, Week or Month

A companion feature to this chart is on the Registration Comparison Events tab.