How do I set up a field so that a change in a calculation in the field does not affect previously created records?
I have a few books on FileMaker development and I remember reading in one of them about how to set up a field so that a calculation change doesn't affect previously created records. For instance, I want to put all of my invoices into one database to make searching easier. But the way my database is set up now, if I change my hourly rate or the tax rates, it changes all of the past invoices as well. I cannot remember what to do to a field so that calculation changes do not affect already created invoices, only newly created ones. Can anyone help, please?