Dart records your task's history, and you can choose to see or hide it. By default, the task history information is hidden, but you can adjust the defaults to show:

You can do this for both dartboards and individual tasks.

To see the history on your dartboards (in list, board, and roadmap layouts; the calendar layout does not show history, although you would be able to click on individual tasks to see sizing once you set that as a defaut), choose the layout dropdown menu from the top right of your screen and then click the "+" to add the history properties you want to see:

In list and roadmap layouts, each history type will show as an individual column:

In board layouts, you will be able to see the information just below the title of the task on the board:

To show task history in individual tasks, go to:

Settings > Properties and click on the history properties you would like to show:

Your history will show below your task title and above your task description, to the left of your task screen: