Single Math N-Back app for seasoned n-back users

What is N-Back:
The N-Back task is a continuous performance task that is frequently used in cognitive neuroscience and psychology assessments to gauge working memory capacity. N-Back games are a training tool that enhances fluid intelligence and working memory.

About this app:
- This is small math n-back app ( it is in single n-back mode and with only plus/minus operators)
- This app just a simple tool without training rules or methods
- This app for seasoned n-back users, who wants more challenge than regular n-back (complete beginners should try other n-back apps first)

Benefits:
- Noticeable multitasking improvement(condition: regular practice in 3digit+ modes) *
- Better abstract visualization (condition: regular practice with "fading" enabled) *
- Improved calculations and remembering numbers
- all other standard n-back benefits(improved working memory, performance boost etc.)

* This benefits is from my own experience and do not represent scientific facts.