Well done, Delia. Most of us have been there. I think I have the T Shirt.Hmmmm... do we have a red-face emoji!!!
Now it's daylight, I thought I'd double-check the batteries were both in the right way round. Grrrr had it wrong, didn't I.
Trouble is the keyboard is black and the + is just a tiny raised mark, so also in black.
I'm back in action but thanks all of you for the help and guidance you've given me.