Well, many thanks to all of you for taking the time to look at my problem although to be honest, some of the discussion was way too complicated for me to understand!



I would just like to say what a great forum this is. So many people willing and able to offer advice to inexperienced users like me. I'm really grateful for your time.

And not at all relevant to your problem.

The take away is....

1. You are right: format the cell as Text first, then enter the long "number" as text.

2. Do not try to use the long "number" in an arithmetic expression; you will lose accuracy. I don't think you would: I presume the long "number" is actually an ID.