At this moment Calculus is available for Android and for Maemo.
Mainly application has 3 screens:
1.- Main screen. It shows a operation, and you have to provide the answer (shown as ? character). Then click on OK button. To remove current answer click on CL button. Once you click on OK button, application will provide you feedback with a Green-Good for right answer, or Red-Bad when answer is wrong.
After two fails, application will show right answer after a Yellow-Lock message.
2.- Options screen. It allows you to select some operations, and level. Level 1 select normal operation (A op B = ?). Level 2 select also operations like A op ? = R. Level 3 show any kind of operation.
3.- Statistics screen. It shows current statistics. Number shown on right means number of failures.