Answer - The fastest free calculator that gives the answer in an instant -

・This app has no “=“ button. As it calculate as you type, you know the answer immediately. ・No problem if you make a mistake. You can tap and correct all your mistakes. As you correct yourself, all calculations are made again, so you get he answer right away. ・As each calculation result will be used for the next calculation, it calculates the same way as a physical calculator. You don't need to think of the calculation order for addition or multiplication. ・You can choose from 19 colors. Use it with your favorite color.