This application is a simple Japanese abacus (soroban / そろばん). It has a free mode where you can use the abacus freely, and a challenge mode with 4 operations (addition, subtraction, one and two digit multiplication, and division) and 3 difficulty levels (easy, medium, hard) where you must race against the clock to perform calculations. Contains tutorials for: * basic concepts * addition * subtraction * one-digit multiplication * two-digit multiplication * division Also has a custom challenge m