Hi, every time we create a job it auto enters a new job number. No problem there.

The boss want that if a job is cancelled and the record deleted the job numbers carry on.

I.e job number 15 is deleted so when we enter a new job the next one would be 15.

can this be done.

Look into the script step Set Next Serial Value.

http://www.filemaker.com/help/html/scripts_ref1.36.41.html#1047759

When a user deletes a record using the Delete button you provide, you can use that script step to reset the serial number assignment for that serial number field using the logic you require.

What if record 13 is deleted... should it be reused again? IN that case the invoice numbers will be 12, 14, 15, 13, 16...

Any process that involves resetting serial numbers opens to risk for duplicates occurring on a multi-user environment.

IMHO either: (1) prevent the records from being deleted and instead mark them as cancelled; or (2) change the boss' mid about having the numbers sequential.

Don't use this invoice number for internal relationships.