Topic: Secrets of the Windows calculator app.
I came across this interesting and maybe useful video about the calculator app that comes with Windows.
https://www.youtube.com/watch?v=PK5WQqN3_44
I use Windows 10, and I don't know if this fully functional app is there in other versions of Windows.
I didn't realise how many things the app does. It calculates in all the obvious ways, including many data functions, it graphs, and is a fairly universal units converter (it even includes US and UK teaspoons).
