A simple fix for this is to add to the begining of your calculation a test isthe date field is empty or not, then running the calc you have when it is.
So modifying your calculation to be the following will solve that.
If ( isEmpty ( ScanDate ) ; "" ; ScanDate - OperationDate )
You could also consideer splitting the scans into a child table, if not already, and thsi will allow you to remove the limit of 6 scans. Unless that is a requirement of your process. Let me know if you need any pointers on doing this
I hope this helps
Thanks Orlando very helpful . Thats worked. A pinter to the child table would be helpful. I am pretty much a novice.
Look up "portal" in FileMaker help or in any training materials you have at hand. You can replace your separate fields with a portal to a related table. You'd create this table in Manage | Database | Tables, define the fields you need in it and then click the Relationships tab to link it to your current table in a relationship.