Use the following *array* formula in Data Validation (Custom)

=PRODUCT((CODE(MID(A1,ROW(1:3),1))64)*(CODE(MID(A 1,ROW(1:3),
1))<=91))*ISNUMBER(--RIGHT(A1,4))*(LEN(A1)=7)

Use Shift+Ctrl+Enter instead of just clicking OK.

HTH
Kostis Vezerides

On Jun 11, 1:59 pm, Sar* wrote:
Hey,

I want to create a validation that when i enter a mixed numeric and alpha
reference that i can prevent changing its format.

For example:

Everytime i enter my "number" FEE1234, that the cell keeps the formatting
"@@@####" and prevents me using any other format indicating n error message.

Cheers!
Thanx in advance
Sar*