The tracker is a chart that displays attributes as horizontal bars that have lengths proportional to the values that they represent.
To learn how to add a new widget, access: https://help.placker.com/en/articles/3078854-how-to-manage-dashboard-widgets
A basic tracker will show the number of cards in a list with a bar chart format. However, it is also possible to change the attribute to show, for example, the number of cards by label.
To change the unit format, sorting and other options, follow the steps in this article: http://help.placker.com/en/articles/3336494-dashboard-common-settings