This is japanese right brain training called Flash Anzan.
You add all numbers popping up one after another.
This mental arithmetic application will make you able to perform hundreds calculations a minute.
If you fall into a slump, you should remember following words.
Don't think. FEEL!(Bruce Lee)
Speed range (2.0秒-0.15秒)
Digit number (1桁-5桁)
Number of calc (5回-300回)
Including negative number or not
Fixed number of digits or not
To save the percentage of questions answered correctly
To retry the previous question
To start again where you left off