Mayan Multiplication

There are no instruction. The opening screen has left/right drag option to use or get info but this does work. You can input lines as per paper method but there's no way of knowing how to get result. Sometimes it appears on its own randomly sometimes it doesn't. Uninstalled.

The grouping algorithm has difficulty interpreting where the different orders of ten are located, and the app doesn't have any instructions on how to best use it (or how to use it at all). Improve useability, and this would be a great trick for the classroom.