Abacus Lesson -ADD and SUB- app analytics for December 29

This is an app that you can learn addition and subtraction using an abacus. An abacus is named "Soroban" in Japan. Do you know what an abacus is? The abacus is very simple calculator used in China, Japan, Korea and so on. Some people may say "Isn't it an unnecessary tool if you have a calculator such as a smartphone?". Answer would be "No". The biggest difference between electric calculators and the abacus is whether you need to hold it in your hand when calculating. Because of its simplicity, you will be able to easily use the abacus in your mind. Imagine that you can use calculations of about 3 digits in your life without physical tools. This app will give you the skill of calculation.