The Matrix Calculator is a free download through the store mobile phones operating with at least a windows 8 system. It also supports at the bare minimum x64, x86, ARM, and ARM64. There are multiple versions that can be downloaded to get exactly what you're looking and stay with the latest updates. Keeps you from having to buy a scientific calculator or a more expensive texas instruments calculator that is bulky and breaks down all the time or runs out of battery. A phone is always with you and it can handle more and more complex tasks aside from just the bare bones operations we learned in grade school.
In conclusion, it is always good to be prepared and be able to do quick calculations at the drop of a hat. You never know when you might need to calculate a bill, tip, or tax. You don't want to be that jerk holding up the line or unable to answer a simple question. And nobody likes to be surprised by how much the total will be at the end of a shopping trip. People always have their phones with them, and this can do more than just add or subtract. Why waste scratch paper or your arm or hand and struggle to find a pencil or pen that writes when a phone's already in your hand. This software is simply a must-have. No brainer.
It's is very convenient to just pop up and access when a math crisis happens in your life.