Hello dear Excel users !

I am doing a database with an output commanded by a data validation drop down list.
This list is varying according to the person browsing the database, as they have different sectors*.

The problem is : someone can type in the name of another sector**, and the display will be calculated even if it's not on the list.
I have set an error message, but it comes too late, after the calculation is made.

I would like to avoid the calculation on the display being made :
- either by preventing users by typing anything in the cell but I need to keep the drop down list button (so I can't protect the sheet and lock the cell)
- either by having the error message before the calculation are being made ? But I do not see how...


If there is another (simple) way, feel free to expose it
Thank you very very much in advance for your help !

Shok

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*example :

Person 1 list :
- Sector A
- Sector B

Person 2 list :
- Sector C
- Sector D

**Person 1 can type in "Sector C" in the cell even if it is not on his data validation list. The display will briefly show the results of Sector C.