Азбука чисел. Ментальная арифм

For whom is this simulator relevant? For children who independently practice mental arithmetic.
For parents teaching their children mental arithmetic.
For teachers and tutors in mental arithmetic.

Topics: Simple, Brother, Friend, Friend + Brother, Anzan.
Speed ​​from 0.1 seconds to 10 seconds.
Bit depth: one-digit, two-digit, three-digit, four-digit.

The simulator is suitable for both adults and children, for all lovers of mental arithmetic.