The statistics screen gives an overview of the status of cards during your learning process. The first bar from the left always represenst the cards that you haven't seen yet. Grey is used to represent cards that are new to you. Red are cards that are expired and can be learned again. The number above a bar gives information of how many cards that are in that range. The height shows the relative distribution of cards of the same range.
Expire Time Statistics shows in how many days a card will expire and should be refreshed. Colors from green to black represents the level of due time within the range of the bar. Black for the lowest side for the cards that will change to the next bar on the left soon.
Recent Encounter Statistics shows how long a card has not been seen.
Time Spacing Statistics shows how many cards are will expire within a day, 1 to 3 days, 3 to 7 days, 7 to 30 days, etc. Red colored are cards that are expired.
Deck Level Statistics shows the cards count for each deck level. There are six deck levels, from 0 to 5. If you decide to use deck level time spacing then the expiration time is determined by the deck level each card belongs to. The second bar are cards that expire after a day, the third after 3 days. The fourth after 1 week, the fifth after 1 month.
The four views can be switched through the menu.