Hi y'all,
I'm keeping a log which will ultimately grow quite lengthy. I've searched through 6 pages of this forum using the keywords allow duplicate, but they're all how to find, remove, etc., which isn't what I'm trying to accomplish,

I don't want the user to be able to enter a serial # (column E) if the serial number has already been entered on another row.

Cpearson's website gives an example, but I must be doing something wrong.
I have substituted =COUNTIF($E$4:$E$200,A4)=1 instead of his example =COUNTIF($A$1:$A$50,A1)=1 but that is telling me duplicate even when it's not. The column with the data that I don't want duplicates allowed is E.

On the Cpearson example above, what does the final A1 do? Does that need to be changed to E something?

Y'all are truly sanity savers and your help has been VERY appreciated each and every time you've helped me. I look forward to your reply.

Thanks -
Ky