Learn progressively by practicing every day

From the most basic level ...
It consists of three levels per operation.
The first level with single-digit operations.
The second level with three-digit operations but still simple.
The third level with three-digit operations but a little more complicated ...

It also provides information on each practice:
 - Number of successes and mistakes
 - Shows errors and corrections
 - It also shows a rating that goes from 0 to 20

It also shows a general report of the whole practice
Date and time of last practice