The main feature of this app is that it generates problems and their solutions. Most study guides have only a few problems and when you're done with them you're not sure you really know how to do the problem. With this app, just hit "New Problem" and a new problem will be generated.....then after you've worked the problem hit "Show Answer" and the answer along with a description of how that answer was arrived at will be displayed. If you want some instruction hit the "Whiteboard" button and an explanation of the concepts involved in the problem you're currently working on will be displayed. Also, the arrow keys take you to extended instruction on the current topic.
The type of problem is selected be moving the selector wheel on the bottom. Start with the first in the list, when you've mastered that go to the next "chapter". The units go from Optical Cross to Transposing, then Combining Lateral and Vertical Prism and ending on Induced Lateral and Vertical Prism. This assumes you have some other instructional material....the main benefit of this is the ability to generate an infinite number of problems.