A=440 is the default of most electronic tuners for stringed instruments and so most guitars banjos and mandolins in folk clubs are there. However, the odd antique squeeze box didn't read the rules. ......

I can usually know the key a song or tune is in by listening but don't have the skills of my late Mum who could tell you most notes on a piano when hearing a single note. C# two octaves above middle C. I can hear her saying it now.