Many, many thanks for your wonderful help. That has worked perfectly. I would
very much like to learn to write complex formulas and wondered as to whether
you could advise a suitable learning resource?

"Elkar" wrote:

Assuming the formula I gave you in your previous post works, you can modify
it like this:

=AND(ISNUMBER(A1),LEN(A1)=10,COUNTIF($A$1:$A$100,A 1)<=1)

Again, change the cell references to meet your needs.

HTH,
Elkar


"SiH23" wrote:

Hi,

I am trying to add validation that willl do the following:

1. Prevent duplicate values being entered into a cell.
2. Only allow a 10 digit number being entered into a cell.

I know how to add these methods individually, but is it possible to set both
validation principles together on a cell or range of cells?

I would be most grateful for any help provided.

Many thanks,

John.