Windows Calculator!
This video is intended to show you that you can still use "Windows Calculator" in Windows 10.
Other versions of windows may also have a working copy of "Windows Calculator" however, I am not sure which versions still have it!
The Windows 10 calculator is a handy tool if you want to do conversions from the old imperial system to the new metric system.
It's also a great tool if you want to check the currency rates to see what you will get for your money when going abroad.
You can also change the type of calculator to things like a "Scientific Mode" or "Programmer Mode" or "Date Calculation Mode".
You can also go into the settings menu and change the colour scheme to dark mode if you like that sort of thing.
You can use it in full screen mode or just as a small compressed box on your screen if you don't want to clutter your screen.
You can also do temperature conversions from "Fahrenheit" to "Celsius" which is handy if you are watching the weather forcast.