The logic of you formula ( SUM?,OR?) totally escapes me
Based on your D6:D13 range following does the trick =AND(MATCH($D6,ID),(COUNTIF($D$6:$D6,$D6)=1)) applied to D6:D13
You were asking for data validation
The value in D10 ( using a formula ) returns FALSE. Entered in the Data Validation wizard it would trigger an error. Thus FALSE is correct
As for D1, you are right I forgot the exact match switch =AND(MATCH($D6,ID,0),(COUNTIF($D$6:$D6,$D6)=1)) which you can use uin the DV now
Yep, D12 that is
No you didn't mention it but other members might think something's wrong. ( as there is no DV implemented as such)
This being said, does this answer your query?
Your solutions of course work very well so thanks to both of you.
However I think I will go with Pecoflyer's solution as it also works and I understand the formula immediately. I have never been that good at VBA and I am just starting to learn about LET.