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.
Visualize custom attribute per card in panel
When you have a widget using effort, budget, story points or a custom attribute as unit of measure, clicking the bar will show not only which cards are counting towards that sum, but also the value of it in the card.
For example, below there are two cards in the done list whose incomes totalize 2721. To see in details how much each of the cards contribute to the total, the panel now shows that one has an income of 1325 and the other 1396:
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