Validate a field with constant prefix

[Bill_misc_IT]

I have a database that tracks manufacturing production. I have a text field that contains a part number (i.e. 123456). The last field in my database is one where I scan a barcode of the part number. I need to validate that the 2 fields match, however, the scanned part number contains of prefix of "P" (i.e. P123456). Previously, I had set the scanned part number field validation as a calculation Exact (part number; "P"&scannned part number). This did the job, but caused some problems during data entry. I'd like to change the validation to a script that is run after data entry. I tried creating a script with:

If Exact (part number; "P"&scannned part number)

task

Else

task

End if

The Exact function is not working anymore?

Please advise