Good app, great study tool! Unfortunately, the "+-" buttons to zoom on visual content like graphs, maps, etc doesn't work when device's nav buttons are present on the screen. Perhaps because the "square" button on the device and the "+-" buttons in the app occupy the same space. Be nice if a "confirm exit" prompt existed for accidental hit of the "back" button too many times. It's too easy to back out of a practice test unintentionally, losing all progress needing restart. 5 star if improved.