Study Session Statistics
Each time you finish a study session you will be presented with the statistics for only that session. At the top you can see the percentage correct for the entire session and then listed below that are the percentages correct for each individual card. The cards are always listed from worst to best and you may at any point select a card and it will change the side of the card that is displayed. This is useful to review any cards that you had any trouble with.
At any point you can find the statistics for any given stack listed next to its name in the main view. You can also find the statistics for each individual card listed next to its name in the stack view.
If you want to reset the statistics for a certain stack you can do so from the settings menu. From that menu you can also reset the statistics on all stacks at the same time.