The app is doing mental arithmetic. The screen changes automatically. You don't have to enter the answer. You are just watching. It is a higher version of "MUGEN ANZAN". -Refresh time can be slowed down to 60 seconds. -The number of digits can be increased (999-6 or 999-37). -The number to add or subtract can be random. -Rotate the device and the display will change to a formula. (screenshots is relatively easy to understand.) Continue to subtract the number and continue to add the number. When it becomes less than the set value, it changes to addition, and when it becomes larger than the set value, it changes to subtraction. Tap the number in the center to start the calculation. When you can calculate and want to proceed quickly, tap the paw pad. (If you want to calculate at your own pace, set a longer time and tap the paw pad to proceed. ) Even if the number to be added or subtracted is fixed, you can change it to another value by tapping the number.